Method and apparatus for communication in wireless mobile communication system

ABSTRACT

Disclosed is a method performed by a terminal, including receiving a first radio resource control (RRC) connection release message for transitioning into an RRC inactive state, the first RRC connection release message including a resume identity and a next hop chaining count, in case that uplink data occurs in the RRC inactive state, transmitting, to a base station, a random access preamble, receiving, from the base station, a random access response including timing alignment information and an uplink grant, transmitting, to the base station, the uplink data with an RRC connection resume request message including the resume identity, and receiving, from the base station, a second RRC connection release message as a response to the RRC connection resume request message.

PRIORITY

This application is a Continuation Application of U.S. patentapplication Ser. No. 15/872,754, which was filed in the U.S. Patent andTrademark Office on Jan. 16, 2018, and claims priority under 35 U.S.C. §119(a) to Korean Patent Application Serial No. 10-2017-0007142, whichwas filed in the Korean Intellectual Property Office on Jan. 16, 2017,and Korean Patent Application Serial No. 10-2017-0029284, which wasfiled in the Korean Intellectual Property Office on Mar. 8, 2017, theentire content of each of which is incorporated herein by reference.

BACKGROUND 1. Field of the Disclosure

The present disclosure relates, generally, to a method and an apparatusin a wireless mobile communication system, and more particularly, to amethod and an apparatus for configuring a packet data convergenceprotocol (PDCP) and a radio link control (RLC) header format in anext-generation mobile communication system, for changing an operationmode of a terminal in a next-generation mobile communication system, forreducing a delay in relation to mobility of a terminal in anext-generation mobile communication system, and for reducing a delayduring a handover in a next-generation mobile communication system.

2. Description of the Related Art

To meet the demand for wireless data traffic using 4G communicationsystems, efforts have been made to develop an improved 5G or pre-5Gcommunication system. The 5G or pre-5G communication system is alsoreferred to as a beyond 4G network or a post long term evolution (LTE)system. The 5G communication system uses higher frequency (mmWave)bands, e.g., 60 GHz bands, to accomplish higher data rates. To decreasepropagation loss of the radio waves and increase the transmissiondistance, beamforming, massive multiple-input multiple-output (MIMO),full dimensional MIMO (FD-MIMO), array antenna, analog beam forming, andlarge scale antenna techniques have been proposed in 5G communicationsystems. In addition, in 5G communication systems, development forsystem network improvement is under way based on advanced small cells,cloud radio access networks (RANs), ultra-dense networks,device-to-device (D2D) communication, wireless backhaul, moving network,cooperative communication, coordinated multi-points (CoMP),reception-end interference cancellation and the like. In the 5Gcommunication system, hybrid frequency-shift keying (FSK) and quadratureamplitude modulation (QAM) (FQAM) and sliding window superpositioncoding (SWSC) as an advanced coding modulation (ACM), and filter bankmulti carrier (FBMC), non-orthogonal multiple access (NOMA), and sparsecode multiple access (SCMA) as an advanced access technology have beendeveloped.

The Internet is now evolving to the Internet of things (IoT) wheredistributed entities exchange and process information without humanintervention. The Internet of everything (IoE), which is a combinationof the IoT technology and the big data processing technology throughconnection with a cloud server, has emerged. As technology elements,such as “sensing technology”, “wired/wireless communication and networkinfrastructure”, “service interface technology”, and “securitytechnology” have been demanded for IoT implementation, a sensor network,a machine-to-machine (M2M) communication, machine type communication(MTC), and so forth have been recently researched. Such an IoTenvironment may provide intelligent Internet technology services bycollecting and analyzing data generated among connected things. IoTs maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing information technology (IT) and variousindustrial applications.

Various attempts have been made to apply 5G communication systems to IoTnetworks. For example, technologies such as a sensor network, MTC, andM2M communication may be implemented by beamforming, MIMO, and arrayantennas. Application of a cloud RAN as the above-described big dataprocessing technology may also be considered as an example ofconvergence between the 5G technology and the IoT technology.

In order to secure a high data rate and to process data at a high speedin a next-generation mobile communication system, a new data processingstructure that may be provided in a PDCP layer, an RLC layer, and a MAClayer may be needed.

If a terminal successively receives and identifies signals of a basestation, terminal power is rapidly consumed. It is important to reducesuch power consumption. Accordingly, the terminal may be switched(transition) from a radio resource control (RRC) connected mode to anRRC idle mode to be in a standby mode. However, many signalingprocedures are necessary in order for the terminal in the standby modeto be switched to the RRC connected mode again.

In the next-generation mobile communication system, an RRC inactive modeor a lightly-connected mode may be defined, in which a rapid accessbecomes possible while reducing the signaling procedure, and theterminal power can be saved as in the standby mode. However, there is aneed for an efficient method for transitioning from the RRC connectedmode to the RRC inactive mode (or lightly-connected mode) and viceversa.

In the RRC inactive mode, a terminal battery power can be saved, andwhen the terminal accesses to a network, a rapid access can beconfigured with a small signaling overhead. However, the terminal in theRRC inactive mode performs a procedure for updating a RAN notificationarea more frequently than a procedure in which the terminal in the RRCidle mode periodically updates a tracking area.

If many terminals in the RRC inactive mode exist in the network, thismay cause the signaling overhead due to the procedure for periodicallyupdating the periodic RAN notification area, and thus it is necessaryfor the network to manage the terminals in the RRC inactive mode and, ifneeded, to switch (transition) the terminals in the RRC inactive mode tothe RRC idle mode.

Further, if a terminal is currently performing a handover in an LTEsystem, synchronization is performed through a random access procedureto a target cell, and the handover procedure is completed throughreception of an uplink grant. In a case of performing theabove-described operation, time interference occurs in the handoverprocedure, and it becomes difficult to satisfy the requirements of thenext-generation mobile communication system requiring a low latency.

SUMMARY

The present disclosure has been made to address at least thedisadvantages described above and to provide at least the advantagesdescribed below.

According to the aspect of the present disclosure, in thenext-generation mobile communication system, a high data rate can besecured, and data can be processed at a high speed.

According to the aspect of the present disclosure, the signalingoverhead can be reduced and the terminal battery can be saved through amethod for switching (transitioning) between the RRC connected mode, theRRC inactive mode (or lightly-connected mode), and the RRC idle modebased on the timer.

According to the aspect of the present disclosure, the terminal cansuspend a discontinuous reception (DRX) operation in relation to ameasurement report, and thus a delay due to the DRX operation can bereduced.

According to the aspect of the present disclosure, in thenext-generation mobile communication system, the handover procedureusing carrier aggregation technology can be used, and, thus, a terminalcan transmit and receive data without time interference during thehandover operation.

In accordance with an aspect of the present disclosure, there isprovided a method performed by a terminal, including receiving a firstradio resource control (RRC) connection release message fortransitioning into an RRC inactive state, the first RRC connectionrelease message including a resume identity and a next hop chainingcount, in case that uplink data occurs in the RRC inactive state,transmitting, to a base station, a random access preamble, receiving,from the base station, a random access response including timingalignment information and an uplink grant, transmitting, to the basestation, the uplink data with an RRC connection resume request messageincluding the resume identity, and receiving, from the base station, asecond RRC connection release message as a response to the RRCconnection resume request message.

In accordance with another aspect of the present disclosure, there isprovided a method performed by a base station in a wirelesscommunication system, including receiving, from a terminal, a randomaccess preamble associated with uplink data for the terminal, theterminal being in an RRC inactive state based on a first RRC connectionrelease message including a resume identity and a next hop chainingcount, transmitting, to the terminal, a random access response includingtiming alignment information and an uplink grant, receiving, from theterminal, the uplink data with an RRC connection resume request messageincluding the resume identity, and transmitting, to the terminal, asecond RRC connection release message as a response to the RRCconnection resume request message.

In accordance with another aspect of the present disclosure, there isprovided a terminal in a wireless communication system, including atransceiver, and a controller configured to receive, via thetransceiver, a first RRC connection release message for transitioninginto an RRC inactive state, the first RRC connection release messageincluding a resume identity and a next hop chaining count, in case thatuplink data occurs in the RRC inactive state, transmit, to a basestation via the transceiver, a random access preamble, receive, from thebase station via the transceiver, a random access response includingtiming alignment information and an uplink grant, transmit, to the basestation via the transceiver, the uplink data with an RRC connectionresume request message including the resume identity, and receive, fromthe base station via the transceiver, a second RRC connection releasemessage as a response to the RRC connection resume request message.

In accordance with another aspect of the present disclosure, there isprovided a base station in a wireless communication system, including atransceiver, and a controller configured to receive, from a terminal viathe transceiver, a random access preamble associated with uplink datafor the terminal, the terminal being in RRC inactive state based on afirst RRC connection release message including a resume identity and anext hop chaining count, transmit, to the terminal via the transceiver,a random access response including timing alignment information and anuplink grant, receive, from the terminal via the transceiver, the uplinkdata with an RRC connection resume request message including the resumeidentity, and transmit, to the terminal via the transceiver, a secondRRC connection release message as a response to the RRC connectionresume request message.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of embodiments ofthe present disclosure will be more apparent from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1A is a diagram of a long-term evolution (LTE) system, according toan embodiment of the present disclosure;

FIG. 1B is a diagram of a radio protocol structure in an LTE system,according to an embodiment of the present disclosure:

FIG. 1C is a diagram of a next-generation mobile communication system,according to an embodiment of the present disclosure:

FIG. 1D is a diagram of a radio protocol structure of a next-generationmobile communication system, according to an embodiment of the presentdisclosure;

FIG. 1E is a flowchart of a method for a terminal that configures anaccess to a network and layer entities to transmit and receive data in anext-generation mobile communication system, according to an embodimentof the present disclosure:

FIG. 1F is a diagram of a method for preprocessing data, according to anembodiment of the present disclosure:

FIG. 1G is a diagram of header formats of a next-generation mobilecommunication system (NR) PDCP device, according to an embodiment of thepresent disclosure;

FIG. 1H is a diagram of header formats of an NR RLC device, according toan embodiment of the present disclosure;

FIG. 1I is a diagram of header structures of bearers to which PDCPheaders and RLC headers are applied, according to an embodiment of thepresent disclosure:

FIG. 1J is a flowchart of a method of a terminal for selecting a PDCPheader and an RLC header of an acknowledged mode (AM) bearer, accordingto an embodiment of the present disclosure:

FIG. 1K is a flowchart of a method of a terminal for selecting a PDCPheader and an RLC header of each bearer, according to an embodiment ofthe present disclosure:

FIG. 1L is a diagram of a terminal, according to an embodiment of thepresent disclosure:

FIG. 1M is a diagram of a base station in a wireless communicationsystem, according to an embodiment of the present disclosure;

FIG. 2A is a diagram of an LTE system, according to an embodiment of thepresent disclosure:

FIG. 2B is a diagram of a radio protocol structure in an LTE system,according to an embodiment of the present disclosure;

FIG. 2C is a diagram of a next-generation mobile communication system,according to an embodiment of the present disclosure:

FIG. 2D is a diagram of a radio protocol structure of a next-generationmobile communication system, according to an embodiment of the presentdisclosure;

FIG. 2E is a of a terminal in a next-generation mobile communicationsystem, according to an embodiment of the present disclosure:

FIG. 2F is a flowchart of method of a terminal switched from an RRCconnected mode to an RRC idle mode and a method of the terminal switchedfrom the RRC idle mode to the RRC connected mode, according to anembodiment of the present disclosure;

FIG. 2G is a flowchart of method of a terminal switched from an RRCconnected mode to an RRC inactive mode or a lightly-connected mode and amethod of the terminal switched from the RRC inactive mode or thelightly-connected mode to the RRC connected mode, according to anembodiment of the present disclosure:

FIG. 2H is a flowchart of a method for switching a terminal from an RRCconnected mode to an RRC inactive mode (or lightly-connected mode),according to an embodiment of the present disclosure;

FIG. 2IA is a flowchart of a method for switching a terminal from an RRCinactive mode (or lightly-connected mode) to an RRC idle mode, accordingto an embodiment of the present disclosure;

FIG. 2IB is a flowchart of a method of a (2-1)-th embodiment forswitching a terminal from an RRC inactive mode (or lightly-connectedmode) to an RRC idle mode, according to an embodiment of the presentdisclosure;

FIG. 2IC is a flowchart of a method of a (2-2)-th embodiment forswitching a terminal from an RRC inactive mode (or lightly-connectedmode) to an RRC idle mode, according to an embodiment of the presentdisclosure:

FIG. 2ID is a flowchart of a method of a (2-3)-th embodiment forswitching a terminal from an RRC inactive mode (or lightly-connectedmode) to an RRC idle mode, according to an embodiment of the presentdisclosure;

FIG. 2J is a diagram of a DRX operation of the terminal, according to anembodiment of the present disclosure;

FIG. 2K is a flowchart of method for switching a terminal from an RRCconnected mode to an RRC inactive mode, according to an embodiment ofthe present disclosure;

FIG. 2L is a flowchart of a method for switching a terminal from an RRCinactive mode to an RRC idle mode, according to an embodiment of thepresent disclosure;

FIG. 2M is a flowchart of a method for switching a terminal from an RRCconnected mode to an RRC inactive mode, according to an embodiment ofthe present disclosure;

FIG. 2N is a flowchart of a method for switching a terminal from an RRCinactive mode to an RRC idle mode, according to an embodiment of thepresent disclosure;

FIG. 2O is a diagram of a terminal, according to an embodiment of thepresent disclosure;

FIG. 2P is a flowchart of a method of a terminal in an RRC inactive modeshifted to an RRC connected mode if downlink data is generated in anetwork, according to an embodiment of the present disclosure;

FIG. 2Q is a flowchart of a method of an access to a network in an RRCinactive mode rejected by the network, according to an embodiment of thepresent disclosure;

FIG. 2R is a flowchart of a method of a terminal in an RRC inactive modenot shifted to an RRC connected mode, but that transmits uplink data inthe RRC inactive mode, according to an embodiment of the presentdisclosure;

FIG. 2S is a flowchart of a method of a terminal in an RRC inactive modenot shifted to an RRC connected mode, but that transmits uplink data inthe RRC inactive mode, according to an embodiment of the presentdisclosure;

FIG. 2T is a flowchart of a method of a terminal in an RRC inactive modenot shifted to an RRC connected mode, but that transmits uplink data inthe RRC inactive mode, according to an embodiment of the presentdisclosure:

FIG. 2U is a of a terminal, according to an embodiment of the presentdisclosure:

FIG. 2V is a diagram of a base station in a wireless communicationsystem, according to an embodiment of the present disclosure:

FIG. 3A is a diagram of an LTE system, according to an embodiment of thepresent disclosure;

FIG. 3B is a diagram of a radio protocol structure in an LTE system,according to an embodiment of the present disclosure;

FIG. 3C is a diagram of a DRX operation of a connected mode in an LTEsystem, according to an embodiment of the present disclosure;

FIG. 3D is a diagram of a delay phenomenon due to a DRX while a handoveris triggered in an LTE system, according to an embodiment of the presentdisclosure;

FIG. 3E is a flowchart of a method for temporarily suspending a DRXwhile a handover is triggered, according to an embodiment of the presentdisclosure:

FIG. 3F is a flowchart of a signaling flow, according to an embodimentof the present disclosure;

FIG. 3G is a flowchart of a method of a terminal, according to anembodiment of the present disclosure;

FIG. 3H is a flowchart of a method of a base station, according to anembodiment of the present disclosure;

FIG. 3I is a diagram of a medium access control MAC control element (CE)indicating a temporal DRX suspend, according to an embodiment of thepresent disclosure;

FIG. 3J is a diagram of a terminal, according to an embodiment of thepresent disclosure;

FIG. 3K is a diagram of a base station, according to an embodiment ofthe present disclosure;

FIG. 4A is a diagram of an LTE system, according to an embodiment of thepresent disclosure:

FIG. 4B is a diagram of a radio protocol structure of an LTE system,according to an embodiment of the present disclosure;

FIG. 4C is a diagram of a carrier aggregation of an LTE system,according to an embodiment of the present disclosure;

FIG. 4D is a diagram of a next-generation mobile communication system,according to an embodiment of the present disclosure;

FIG. 4E is a flowchart of a handover procedure of an LTE system,according to an embodiment of the present disclosure;

FIGS. 4FA and 4FB are diagrams of a handover operation using enhancedcarrier aggregation (eCA) and a protocol structure, according to anembodiment of the present disclosure;

FIGS. 4GA and 4GB are diagrams of a handover procedure using eCA,according to an embodiment of the present disclosure;

FIG. 4H is a flowchart of a method of the terminal performing type-2handover procedure using eCA, according to an embodiment of the presentdisclosure;

FIG. 4I is a diagram of a terminal, according to an embodiment of thepresent disclosure; and

FIG. 4J is a diagram of an NR base station, according to an embodimentof the present disclosure.

DETAILED DESCRIPTION

In describing embodiments of the present disclosure, explanation oftechnical contents which are well known in the art to which the presentdisclosure pertains and are not directly related to the presentdisclosure will be omitted. This is to transfer the subject matter ofthe present disclosure more clearly without obscuring the same throughomission of unnecessary explanations.

For the same reason, in the accompanying drawings, sizes and relativesizes of some constituent elements may be exaggerated, omitted, orbriefly illustrated. Further, sizes of the respective constituentelements do not completely reflect the actual sizes thereof. In thedrawings, the same drawing reference numerals are used for the same orcorresponding elements across various figures.

The advantages and features of the present disclosure and the manner ofachieving them will become apparent with reference to the embodimentsdescribed in detail below with reference to the accompanying drawings.The present disclosure may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of thepresent disclosure to those skilled in the art. To fully disclose thescope of the present disclosure to those skilled in the art, and thepresent disclosure is only defined by the scope of the claims.

It will be understood that each block of the flowchart illustrations,and combinations of blocks in the flowchart illustrations, may beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which are executed via the processor of the computer or otherprogrammable data processing apparatus, generate means for implementingthe functions specified in the flowchart block or blocks. These computerprogram instructions may also be stored in a computer usable orcomputer-readable memory that may direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer usable orcomputer-readable memory produce an article of manufacture includinginstruction means that implement the function specified in the flowchartblock or blocks. The computer program instructions may also be loadedonto a computer or other programmable data processing apparatus to causea series of operations to be performed on the computer or otherprogrammable apparatus to produce a computer implemented process suchthat the instructions that are executed on the computer or otherprogrammable apparatus provide operations for implementing the functionsspecified in the flowchart block or blocks.

And each block of the flowchart illustrations may represent a module,segment, or portion of code, which comprises one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that in some alternative implementations, thefunctions noted in the blocks may occur out of the order. For example,two blocks shown in succession may in fact be executed substantiallyconcurrently or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

The term “unit”, as used herein, may refer to a software or hardwarecomponent or device, such as a field programmable gate array (FPGA) orapplication specific integrated circuit (ASIC), which performs certaintasks. A unit may be configured to reside on an addressable storagemedium and configured to execute on one or more processors. Thus, amodule or unit may include, by way of example, components, such assoftware components, object-oriented software components, classcomponents and task components, processes, functions, attributes,procedures, subroutines, segments of program code, drivers, firmware,microcode, circuitry, data, databases, data structures, tables, arrays,and variables. The functionality provided for in the components andmodules/units may be combined into fewer components and modules/units orfurther separated into additional components and modules.

Hereinafter, terms for identifying a connection node, terms for callingnetwork entities, terms for calling messages, terms for calling aninterface between network entities, and terms for calling various piecesof identification information, as used herein, are for convenience ofexplanation. Accordingly, the present disclosure is not limited to theterms to be described later, but other terms for calling subjects havingequal technical meanings may be used.

Hereinafter, terms and titles that are defined in the 3^(rd) generationpartnership project (3GPP) LTE standards are used in the presentdisclosure. However, the present disclosure is not limited by the termsand titles, but can be equally applied to systems following otherstandards. For convenience of explanation, evolved node B (eNB) may beused interchangeably with gateway node B (gNB). That is, a base stationexplained as eNB may be denoted as gNB. Further, the base station mayinclude a transmission and reception point (TRP).

Embodiment 1

FIG. 1A is a diagram of an LTE system, according to an embodiment of thepresent disclosure.

Referring to FIG. 1A, a RAN of an LTE system includes evolved node Bs(“eNBs” “ENBs, “node Bs”, or “base stations”) 1 a-05, 1 a-10, 1 a-15,and 1 a-20, a mobility management entity (MME) 1 a-25, and aserving-gateway (S-GW) 1 a-30. User equipment (“UE” or “terminal”) 1a-35 accesses to an external network through the ENBs 1 a-05, 1 a-10, 1a-15, and 1 a-20 and the S-GW 1 a-30.

The ENBs 1 a-05, 1 a-10, 1 a-15, and 1 a-20 correspond to an existingnode B of a universal mobile telecommunications system (UMTS). The ENBs1 a-05, 1 a-10, 1 a-15, or 1 a-20 are connected to the UE 1 a-35 on aradio channel, and play or serve a more complicated role than that ofthe existing node B. In the LTE system, since all user trafficsincluding a real-time service, such as a voice over internet protocol(VoIP) through an internet protocol, are serviced on shared channels,devices performing scheduling through summarization of stateinformation, such as a buffer state, an available transmission powerstate, and a channel state of each UE, are necessary, and the ENBs 1a-05, 1 a-10, 1 a-15, and 1 a-20 correspond to such scheduling devices.One ENB controls a plurality of cells. In order to implement atransmission speed of 100 Mbps, the LTE system uses orthogonal frequencydivision multiplexing (OFDM) in a bandwidth of 20 MHz as a radio accesstechnology (RAT). The LTE system adopts an adaptive modulation & coding(AMC) scheme that determines a modulation scheme and a channel codingrate to match the channel state of the terminal. The S-GW 1 a-30provides a data bearer, and generates or removes the data bearer underthe control of the MME 1 a-25. The MME 1 a-25 takes charge of orcontrols not only mobility management of the UE 1 a-35, but also variouskinds of control functions, and is connected to the plurality of ENBs 1a-05, 1 a-10, 1 a-15, and 1 a-20.

FIG. 1B is a diagram of a radio protocol structure in an LTE system,according to an embodiment of the present disclosure.

Referring to FIG. 1B, in a UE or an ENB, a radio protocol of an LTEsystem includes a PDCP 1 b-05 or 1 b-40, an RLC 1 b-10 or 1 b-35, and aMAC 1 b-15 or 1 b-30. The PDCP 1 b-05 or 1 b-40 takes charge of IPheader compression/decompression operations. The main functions of thePDCP are summarized as follows:

-   -   Header compression and decompression: robust header compression        (ROHC) only;    -   Transfer of user data;    -   In-sequence delivery of upper layer physical data units (PDUs)        at a PDCP reestablishment procedure for an RLC AM;    -   For split bearers in dual connectivity (DC) (only support for an        RLC AM): PDCP PDU routing for transmission and PDCP PDU        reordering for reception;    -   Duplicate detection of lower layer service data units (SDUs) at        a PDCP reestablishment procedure for an RLC AM;    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at a PDCP data-recovery procedure, for an        RLC AM;    -   Ciphering and deciphering; and    -   Timer-based SDU discard in an uplink; The RLC 1 b-10 or 1 b-35        reconfigures a PDCP PDU with a proper size and performs an        automatic repeat request (ARQ) operation and the like. The main        functions of the RLC are summarized as follows.    -   Transfer of upper layer PDUs;    -   Error correction through an ARQ (only for AM data transfer);    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for unacknowledged mode (UM) and AM data transfer);    -   Re-segmentation of RLC data PDUs (only for UM and AM data        transfer);    -   Reordering of RLC data PDUs (only for UM and AM data transfer);    -   Duplicate detection (only for UM and AM data transfer);    -   Protocol error detection (only for AM data transfer);    -   RLC SDU discard (only for UM and AM transfer); and    -   RLC reestablishment.

The MAC 1 b-15 or 1 b-30 is connected to several RLC layer devicesconfigured in one terminal, and performs multiplexing/demultiplexing ofRLC PDUs into/from MAC PDU. The main functions of the MAC are summarizedas follows:

-   -   Mapping between logical channels and transport channels;    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        transferred to/from the physical layer on transport channels;    -   Scheduling information reporting;    -   Hybrid ARQ (HARQ) function (error correction through HARQ);    -   Priority handling between logical channels of one UE;    -   Priority handling between UEs by means of dynamic scheduling;    -   MBMS service identification;    -   Transport format selection; and    -   padding.

The physical layer 1 b-20 or 1 b-25 performs channel coding andmodulation of upper layer data to configure and transmit OFDM symbols ona radio channel, or performs demodulation and channel decoding of theOFDM symbols received on the radio channel to transfer the demodulatedand channel-decoded symbols to an upper layer.

FIG. 1C is a diagram of a next-generation mobile communication system,according to an embodiment of the present disclosure.

Referring to FIG. 1C, a RAN of a next-generation mobile communicationsystem (“new radio (NR)” or “5G”) is composed of a new radio node B (“NRgNB” or “NR ENB”) 1 c-10 and a new radio core network (NR CN) 1 c-05. Anew radio user equipment (“NR UE” or “terminal”) 1 c-15 accesses to anexternal network through the NR gNB 1 c-10 and the NR CN 1 c-05.

The NR gNB 1 c-10 corresponds to an ENB of the existing LTE system. TheNR gNB is connected to the NR UE 1 c-15 on a radio channel, and, thus,it can provide a more superior service than the service of the existingnode B. Since all user traffics are serviced on shared channels in thenext-generation mobile communication system, a device that performsscheduling through consolidation of status information, such as a bufferstate of UEs, an available transmission power state, and a channelstate, is required, and the NR NB 1 c-10 takes charge of this.

One NR gNB 1 c-10 generally controls a plurality of cells. In order toimplement ultrahigh-speed data transmission as compared with theexisting LTE, the NR gNB may have a bandwidth that is equal to or higherthan the existing maximum bandwidth, and a beamforming technology may beadditionally grafted in consideration of OFDM) as a RAT. An AMC schemedetermining a modulation scheme and a channel coding rate to match thechannel state of the UE is adopted. The NR CN 1 c-05 performs functionsof mobility support, bearer setup, and quality of service (QoS)configuration. The NR CN 1 c-05 is a device that takes charge of notonly a mobility management function of the UE 1 c-15 but also variouskinds of control functions, and is connected to a plurality of ENBs. Thenext-generation mobile communication system may interlock with theexisting LTE system, and the NR CN 1 c-05 is connected to an MME 1 c-25through a network interface. The MME 1 c-25 is connected to an ENB 1c-30 that is the existing ENB.

FIG. 1D is a diagram of a radio protocol structure of a next-generationmobile communication system, according to an embodiment of the presentdisclosure.

Referring to FIG. 1D, in a UE or an NR ENB, a radio protocol of thenext-generation mobile communication system includes an NR PDCP 1 d-05or 1 d-40, an NR RLC 1 d-10 or 1 d-35, and an NR MAC 1 d-15 or 1 d-30.

The main functions of the NR PDCP 1 d-05 or 1 d-40 may include parts ofthe following functions:

-   -   Header compression and decompression: ROHC only;    -   Transfer of user data;    -   In-sequence delivery of upper layer PDUs;    -   PDCP PDU reordering for reception;    -   Duplicate detection of lower layer SDUs;    -   Retransmission of PDCP SDUs;    -   Ciphering and deciphering; and    -   Timer-based SDU discard in an uplink.

Reordering of the NR PDCP devices may include reordering of PDCP PDUsreceived from a lower layer based on PDCP sequence numbers (SNs). Thereordering may include transfer of data to an upper layer in the orderof reordering, recording of lost PDCP PDUs through reordering, statusreport for the lost PDCP PDUs to a transmission side, and retransmissionrequest for the lost PDCP PDUs.

The main functions of the NR RLC 1 d-10 or 1 d-35 may include parts ofthe following functions:

-   -   Transfer of upper layer PDUs;    -   In-sequence delivery of upper layer PDUs;    -   Out-of-sequence delivery of upper layer PDUs;    -   Error correction through an ARQ;    -   Concatenation, segmentation, and reassembly of RLC SDUs;    -   Re-segmentation of RLC data PDUs;    -   Reordering of RLC data PDUs;    -   Duplicate detection;    -   Protocol error detection;    -   RLC SDU discard; and    -   RLC reestablishment.

In-sequence delivery of NR RLC devices may include in-sequence deliveryof RLC SDUs received from a lower layer to an upper layer. When oneoriginal RLC SDU is segmented into several RLC SDUs to be received, thedelivery may include reassembly and delivery of the RLC SDUs, reorderingof the received RLC PDUs based on an RLC SN or a PDCP SN, recording oflost RLC PDUs through reordering, status report for the lost RLC PDUs toa transmission side, retransmission request for the lost PDCP PDUs,in-sequence delivery of only RLC SDUs just before the lost RLC SDU to anupper layer if there is the lost RLC SDU, in-sequence delivery of allRLC SDUs received before a specific timer starts its operation to anupper layer if the timer has expired although there is the lost RLC SDU,or in-sequence delivery of all RLC SDUs received up to now to an upperlayer if the timer has expired although there is the lost RLC SDU. TheNR RLC layer may not include a concatenation function, and the functionmay be performed by an NR MAC layer or may be replaced by a multiplexingfunction of the NR MAC layer.

The out-of-sequence delivery of the NR RLC device includes transferringthe RLC SDUs received from a lower layer directly to an upper layer inan out-of-sequence manner. If one original RLC SDU is segmented intoseveral RLC SDUs to be received, the delivery may include reassembly anddelivery of the RLC SDUs, and recording of the lost RLC PDUs throughstoring and ordering the RLC SNs or PDCP SNs of the received RLC PDUs.

The NR MAC 1 d-15 or 1 d-30 may be connected to several NR RLC layerdevices configured in one UE, and the main functions of the NR MAC 1d-15 or 1 d-30 may include parts of the following functions:

-   -   Mapping between logical channels and transport channels;    -   Multiplexing/demultiplexing of MAC SDUs;    -   Scheduling information reporting;    -   HARQ function (error correction through HARQ);    -   Priority handling between logical channels of one UE;    -   Priority handling between UEs by means of dynamic scheduling;    -   MBMS service identification;    -   Transport format selection;    -   padding.

The NR PHY layer 1 d-20 or 1 d-25 may perform channel coding andmodulation of upper layer data to configure and transmit OFDM symbols toa radio channel, or may perform demodulation and channel decoding of theOFDM symbols received on the radio channel to transfer the demodulatedand channel-decoded symbols to an upper layer.

FIG. 1E is a flowchart of a method for a terminal that configures anaccess to a network and layer entities to transmit and receive data in anext-generation mobile communication system, according to an embodimentof the present disclosure.

If data to be transmitted is generated, a UE (idle mode UE) 1 e-01, ofwhich connection is not currently set, performs an RRC connectionestablishment process with an LTE ENB or NR ENB 1 e-02. The UE 1 e-01establishes backward transfer synchronization with the ENB 1 e-02through a RAP, and transmits an RRCConnectionRequest message to the ENB1 e-02 (at step 1 e-05). The message contains an identifier of the UE 1e-01 and a cause for connection setup.

The ENB 1 e-02 transmits an RRCConnectionSetup message to the UE 1 e-01so that the UE 1 e-01 sets the RRC connection (at step 1 e-10). Themessage may contain RRC connection setup information and setupinformation of respective layers. That is, the message may include setupinformation about a PHY or NR PHY device, a MAC or NR MAC device, an RLCor NR RLC device, and a PDCP or NR PDCP device, and may includeinformation indicating setup for a specific one of functions supportedby the layer entities (layer functions as described above with referenceto FIG. 1B or 1D). The message may include setup information to beapplied by the PDCP device and the RLC device through a bearer setup,and may include information (or indication) indicating the length of aSN and information on what PDCP header format and what RLC header formatare to be applied.

The UE 1 e-01 having set an RRC connection transmits anRRCConnectionSetupComplete message to the ENB 1 e-02 (at step 1 e-15).In order to set a data radio bearer (DRB), the ENB 1 e-02 transmits anRRCConnectionReconfiguration message to the UE 1 e-01 (at step 1 e-20).The message may contain setup information of respective layers. That is,the message may include setup information about the PHY or NR PHYdevice, the MAC or NR MAC device, the RLC or NR RLC device, and the PDCPor NR PDCP device, and may include information indicating the setup fora specific one of functions supported by the layer entities (layerfunctions as described above with reference to FIG. 1B or 1D). Themessage may include the setup information to be applied by the PDCPdevice and the RLC device through the bearer setup, and may includeinformation (or indication) indicating the length of the SN andinformation on what PDCP header format and what RLC header format are tobe applied. The message includes setup information of the DRB throughwhich user data is to be processed, and the UE 1 e-01 sets the DRB byapplying the information, sets respective layer functions, and transmitsan RRCConnectionReconfigurationComplete message to the ENB 1 e-02 (atstep 1 e-25).

If the above-described processes are all completed, the UE 1 e-01transmits/receives data to/from the ENB 1 e-02 (at step 1 e-30). Duringtransmission/reception of the data, if needed, the ENB 1 e-02 may resendthe RRCConnectionReconfiguration message to the UE 1 e-01 (at step 1e-35) to reconfigure the setup information of the respective layers ofthe UE. That is, the message may include the setup information about thePHY or NR PHY device, the MAC or NR MAC device, the RLC or NR RLCdevice, and the PDCP or NR PDCP device, and may include the informationindicating the setup for a specific one of functions supported by thelayer entities (layer functions as described above with reference toFIG. 1B or 1D). The message may include the setup information to beapplied by the PDCP device and the RLC device through the bearer setup,and may include information (or indication) indicating the length of theSN and information on what PDCP header format and what RLC header formatare to be applied. If the setup of the respective layer entities iscompleted in accordance with the message, the UE 1 e-01 transmits theRRCConnectionReconfigurationComplete message to the ENB 1 e-02 (at step1 e-40).

FIG. 1F is a diagram of a method for preprocessing data, according to anembodiment of the present disclosure.

In the next-generation mobile communication system, if an NR ENB or a UEon a user plane receives a data packet 1 f-05 from an upper layer, itmay preprocess the received packet. The data preprocessing includespreprocessing an IP packet to a PDCP PDU 1 f-10 of a PDCP layer, an RLCPDU 1 f-15 of an RLC layer, or a MAC SDU 1 f-20 of a MAC layer togetherwith a MAC sub-header.

FIG. 1G is a diagram of header formats of an NR PDCP device, accordingto an embodiment of the present disclosure.

In FIG. 1G, 1 g-05 representing the first PDCP header format for acontrol plane of a PDCP device may support an SN having a length of 6bits, and may have a reservation field of 2 bits. 1 g-10 representingthe (2-1)-th PDCP header format for a user plane of the PDCP device maysupport an SN of 6 bits, and may have a reservation field of 1 bit and aD/C field of 1 bit. The D/C field is a field for discrimination betweena PDCP control PDU sending/receiving a control command between PDCPdevices and a PDCP data PDU received from an upper layer. 1 g-15representing the (2-2)-th PDCP header format for the user plane of thePDCP device may support an SN of 8 bits, and may have a reservationfield of 5 bits and a D/C field of 1 bit. The D/C field is a field fordiscrimination between the PDCP control PDU sending/receiving thecontrol command between the PDCP devices and a PDCP data PDU receivedfrom the upper layer. 1 g-20 representing the (2-3)-th PDCP headerformat for the user plane of the PDCP device may support an SN of 18bits, and may have a reservation field of 5 bits and a D/C field of 1bit. The D/C field is a field for discrimination between the PDCPcontrol PDU sending/receiving the control command between the PDCPdevices and a PDCP data PDU received from the upper layer.

When defining the PDCP header as described above, one header for thecontrol plane has been defined as the first PDCP header format, andthree headers for the user plane have been defined as the (2-1)-th,(2-2)-th, and (2-3)-th PDCP header formats. However, using theabove-described fields, x PDCP headers for the control plane may bedefined, and y PDCP headers for the user plane may be defined. Althoughthe PDCP SNs respectively support 6 bits, 10 bits, and 18 bits asdescribed above, a PDCP SN having specific k bits may be additionallysupported.

FIG. 1H is a diagram of header formats of an NR RLC device, according toan embodiment of the present disclosure.

In FIG. 1H, 1 h-05 representing the first RLC header format for an RLCunacknowledged mode (UM) of an RLC device may support an SN having alength of 6 bits, and may have a segmentation information (SI) field of2 bits. The SI field may be defined as follows, and the field name SImay be named another name, such as frame information (FI) orsegmentation control (SC).

TABLE 1 Value Description 00 A complete RLC PDU 01 First segment of aRLC PDU 10 Last segment of a RLC PDU 11 Middle segment of a RLC PDU

If the SI field is 00, it represents a complete RLC PDU that is notsegmented, and in this case, the RLC header does not require a segmentoffset (SO) field. If the SI field is 01, it represents the foremost RLCPDU segment that is segmented, and in this case, the RLC header does notrequire the SO field. If the SI field is 10, it represents the last RLCPDU segment that is segmented, and in this case, the RLC header requiresthe SO field. If the SI field is 11, it represents the middle RLC PDUsegment that is segmented, and in this case, the RLC header requires SOfield. The number of mapping relations between the 2 bits and the fourkinds of information (complete RLC PDU, foremost segment, last segment,and middle segment) is 24 (=4×3×2×1) in total, and the above-describedexample indicates one of them. 24 kinds of mappings are included. The SOfields are 15 or 16 fields, and are used to indicate at what position onthe original PDU the PDU segment exists.

The SI field of 2 bits may be replaced by a segment flag (SF) field of 1bit and a last segment flag (LSF) field of 1 bit. The SF field of 1 bitmay indicate existence/nonexistence of the segment in the RLC PDU, andthe LSF field of 1 bit may be a field indicating whether the segment isthe last segment of the original RLC PDU. That is, if the SF field is 0,the segment does not exist, whereas if the SF field is 1, the segmentexists. This may also be defined through changing of 0 and 1 with eachother. If the LSF field is 0, it may be indicated that the segment isthe first or middle segment, or it may be indicated that the segment isonly the first segment or only the middle segment. If the LSF field is1, it may be indicated that the segment is the last segment. Further,this may also be defined through changing 0 and 1 with each other. TheSF field of 1 bit and the LSF field of 1 bit as defined above may alwaysexist in the RLC header.

The SI field of 2 bits may be replaced by the SF field of 1 bit and theLSF field of 1 bit. The SF field of 1 bit indicatesexistence/nonexistence of the segment in the RLC PDU, and if it isindicated that the segment exists, the LSF field also exists at the sametime. Accordingly, if the SF field indicates nonexistence of thesegment, even the LSF field may not exist. That is, if the SF field is0, it may indicate that the segment does not exist and the LSF fielddoes not exist at the same time. Accordingly, only when the SF field is1, that is, the segment exists, the LSF field may also exist, and if theLSF field is 0, it may indicate that the segment is not the lastsegment, whereas if the LSF field is 1, it may indicate that the segmentis the last segment. Accordingly, the SF field always exists in the RLCheader, but the LSF field may exist only when the segment exists in theSF field.

Further, 1 h-10 representing the (2-1)-th RLC header format for an RLCAM of the RLC device may support an SN of 10 bits, and may have a D/Cfield of 1 bit, an SI field of 2 bits, a polling field of 1 bit, and areservation field of 2 bits. The D/C field is a field for discriminationbetween an RLC control PDU sending/receiving a control command betweenRLC devices and an RLC data PDU received from an upper layer. Thepolling field is a field for requesting an RLC buffer status report.

1 h-15 representing the (2-2)-th RLC header format for the RLC AM of theRLC device may support an SN of 18 bits, and may have a D/C field of 1bit, an SI field of 2 bits, a polling field of 1 bit, and a reservationfield of 2 bits. The D/C field is a field for discrimination between anRLC control PDU sending/receiving a control command between RLC devicesand an RLC data PDU received from an upper layer. The polling field is afield for requesting an RLC buffer status report.

When defining the RLC header as described above, one header for the RLCUM has been defined as the first RLC header format, and two headers forthe RLC AM have been defined as the (2-1)-th and (2-2)-th RLC headerformats. However, using the above-described fields, m RLC headers forthe RLC UM mode may be defined, and n RLC headers for the RLC AM modemay be defined. Although the PDCP SN s respectively support 6 bits, 10bits, and 18 bits as described above, an RLC SN having specific x bitsmay be additionally supported.

In the next-generation mobile communication system, the RLC layer doesnot have a concatenation function, and, thus, it is characteristic ofthe next-generation mobile communication system that the RLC header doesnot have an E field. In a legacy mobile communication system, the Efield is an information field that indicates whether a data field comesjust behind an anchor RLC header part of the header or the E field, orwhether the E field, an L field, or another header field comes justbehind the anchor RLC header part or the E field. If the E field is 0,it indicates whether the data field comes just behind the anchor RLCheader part or the E field, whereas if the E field is 1, it indicateswhether another E field, the L field, or another header field comes justbehind the anchor RLC header part or the E field. In the next-generationmobile communication system, when indicating segments, the RLC layer canuse an integrated segmentation method based on the SO field, and, thus,it may not be necessary to discriminate between segmentation andre-segmentation, and it may not be necessary to particularly indicatethe segment. Accordingly, the RLC header may be featured not to have are-segmentation flag field. The re-segmentation flag field is composedof 1 bit, and is used to indicate whether the configured RLC PDU is aPDU or a PDU segment.

FIG. 1I is a diagram of bearers of PDCP headers and RLC headers areapplied, according to an embodiment of the present disclosure.

Referring to FIG. 1I, when a signaling radio bearer (SRB) in thenext-generation mobile communication system (1 i-05), since it ispossible to transmit/receive data on a control plane and to apply theRLC AM mode, the first PDCP header and the (2-1)-th RLC header can beused. When a UM bearer for VoIP or audio or video streaming (1 i-10),the (2-1)—the PDCP header and the first RLC header can be applied. Whena general AM bearer (1 i-15 or 1 i-20), the (2-2)-th PDCP header and the(2-1)—the RLC header may be applied (1 i-15), or the (2-3)-th PDCPheader and the (2-2)-th RLC header may be applied (1 i-20).

In the next-generation mobile communication system, the RLC header andthe PDCP header may use a SN having the same length when they areapplied to a certain bearer, a DRB or an SRB. The SRB bearer may use aSN having a different length.

When using the PDCP headers and the RLC headers of FIGS. 1G and 1H, onlyone combination of the PDCP header and the RLC header exists in the SRBbearer and the UM bearer. Accordingly, it may be directly applied to thePDCP device and the RLC device. However, when the AM bearer, twocombinations of the PDCP header and the RLC header exist, a method forselecting one of them is required.

A first embodiment for selecting the PDCP header and the RLC header ofthe AM bearer is as follows.

If the AM bearer receives an RRC message (e.g., 1 e-10, 1 e-20, or 1e-35 of FIG. 1E), and if a first condition is satisfied, a first methodis applied, whereas if a second condition is satisfied, a second methodis applied.

The first condition corresponds to a case where information (indication)indicating the SN is included in information for configuring the PDCPdevice and the RLC device of the bearer (the information for configuringthe PDCP device and the RLC device may be included and indicated in theRRC message 1 e-10, 1 e-20, or 1 e-35 in FIG. 1E).

The second condition corresponds to a case where the information(indication) indicating the SN is not included in the information forconfiguring the PDCP device and the RLC device of the bearer.

The first method includes an application of the (2-2)-th PDCP header andthe (2-1)-th RLC header in the AM bearer (1 i-15), and the second methodincludes an application of the (2-3)-th PDCP header and the (2-2)-th RLCheader in the AM bearer (1 i-20).

FIG. 1J is a flowchart of a method of a terminal for selecting a PDCPheader and an RLC header of an AM bearer when using the PDCP headers andthe RLC headers proposed of FIGS. 1G and 1H, according to an embodimentof the present disclosure.

A terminal 1 j-01 receives an RRC message at step 1 j-05 (e.g., 1 e-10,1 e-20, or 1 e-35 of FIG. 1E), and if a first condition is satisfied atstep 1 j-10, a first method is applied (at step 1 j-15), whereas if asecond condition is satisfied, a second method is applied (at step 1j-20).

In contrast with the PDCP headers and the RLC headers proposed in FIGS.1G and 1H, various PDCP headers and RLC headers can be defined usingrespective PDCP header fields and RLC header fields. In this case, sincetwo or more combinations of the PDCP header and the RLC header may existin an SRB bearer, a UM bearer, and an AM bearer, a procedure ofselecting header formats of the respective PDCP devices and RLC devicesis necessary. A second embodiment for selecting the PDCP header and theRLC header of the PDCP device and the RLC device is as follows.

A base station may send a radio bearer (RB) setup message to a terminal.The message may be included and indicated in an RRC message (1 e-10, 1e-20, or 1 e-35 of FIG. 1E). The terminal receives the message, sets upa bearer, and determines a format of packets to be transmitted andreceived through the bearer. The terminal and the base stationtransmit/receive data packets to/from each other in the determinedformat. In this case, a second embodiment for determining header formatsof the PDCP device and the RLC device of the packets to be transmittedand received of the bearer is as follows.

The terminal may receive an RRC message, e.g., 1 e-10, 1 e-20, or 1 e-35of FIG. 1E, and if a first condition and a second condition aresatisfied, a first method may be applied, whereas if the first conditionand a third condition are satisfied, a second method may be applied. Ifa fourth condition is satisfied, a third method may be applied, and if afifth condition is satisfied, a fourth method may be applied. If a sixthcondition is satisfied, a fifth method may be applied, and if a seventhcondition is satisfied, a sixth method may be applied. If an eighthcondition is satisfied, a seventh method may be applied, and if a ninthcondition is satisfied, an eighth method may be applied.

The first condition as described above corresponds to a case where theRB is a DRB and the RB setup message does not include informationindicating the length of a SN, and the second condition corresponds to acase where the RB is an RLC AM bearer (or an RLC AM mode is applied).The third condition corresponds to a case where the RB is an RLC UMbearer (or an RLC UM mode is applied), and the fourth conditioncorresponds to a case where the RB is a DRB and the RB setup messageincludes only information indicating the length of a PDCP sequencenumber. The fifth condition corresponds to a case where the RB is a DRBand the RB setup message includes both information indicating the lengthof a PDCP SN and information indicating the length of an RLC SN, and thesixth condition corresponds to a case where the RB is a control bearer(e.g., SRB), and the RB setup message does not include informationindicating the length of a SN. The seventh condition corresponds to acase where the RB is a control bearer and the RB setup message includesinformation indicating the length of an RLC SN, and the eighth conditioncorresponds to a case where the RB is a control bearer and the RB setupmessage includes information indicating the length of a PDCP SN. Theninth condition corresponds to a case where the RB is a control bearerand the RB setup message includes information indicating the length of aPDCP SN and the length of an RLC SN.

The first method as described above is to configure the length of thePDCP SN and the length of the RLC SN with specific n bits, and thesecond method is to configure the length of the PDCP SN and the lengthof the RLC SN with specific m bits. The third method is to configure thelength of the RLC SN to be equal to the length of the PDCP SN, and thefourth method is to configure the length of the PDCP SN and the lengthof the RLC SN with indicated values. The fifth method is to configurethe length of the PDCP SN with specific k bits and to configure thelength of the RLC SN with specific j bits (where, k and j may bedifferent from each other), and the sixth method is to use specific kbits for the length of the PDCP SN and to use an indicated size for thelength of the RLC SN. The seventh method is to use an indicated size forthe length of the PDCP SN and to use the same length as the length ofthe PDCP SN for the RLC SN, and the eighth method is to use an indicatedsize for the length of the PDCP SN and to use an indicated size also forthe length of the RLC SN.

The information for configuring the PDCP device and the RLC device inthe RB setup message may be included and indicated in the RRC message(e.g., 1 e-10, 1 e-20, or 1 e-35 of FIG. 1E).

The second embodiment for selecting the header formats of the PDCPdevice and the RLC device as described above may be summarized asfollows:

When the radio bearer is a DRB, and the RB setup message does notinclude the information indicating the length of the SN,

-   -   if the RB is the RLC AM bearer, the length of the PDCP SN and        the length of the RLC SN are configured with specific n bits,        and    -   if the RB is the RLC UM bearer, the length of the PDCP SN and        the length of the RLC SN are configured with specific m bits.    -   When the RB is a DRB, and the RB setup message includes only the        information indicating the length of the PDCP SN,    -   the length of the RLC SN is configured to be equal to the length        of the PDCP SN.

When the RB is a DRB, and the RB setup message includes both theinformation indicating the length of the PDCP SN and the informationindicating the length of the RLC SN,

-   -   the length of the RLC SN is configured to be an indicated value.

When the RB is an SRB, and the RB setup message does not include theinformation indicating the length of the SN,

-   -   the length of the PDCP SN is composed of specific k bits, and    -   the length of the RLC SN is composed of specific j bits (where,        k and j may be different from each other).

When the RB is an SRB, and the RB setup message includes the informationindicating the length of the RLC SN,

-   -   the length of the PDCP SN is composed of specific k bits, and    -   the length of the RLC SN is configured to have an indicated        size.

When the RB is an SRB, and the RB setup message includes the informationindicating the length of the PDCP SN,

-   -   the length of the PDCP SN has an indicated size, and    -   the RLC SN uses the length of the SN equal to that of the PDCP.

When the RB is an SRB, and the RB setup message includes the informationindicating the length of the PDCP SN and the length of the RLC SN,

-   -   the length of the PDCP SN has an indicated size, and    -   the RLC SN has an indicated size.

FIG. 1K is a flowchart of a method of a terminal for selecting a PDCPheader and an RLC header of each bearer using various PDCP headers andRLC headers, according to an embodiment of the present disclosure.

Referring to FIG. 1K, a terminal at step 1 k-01 receives an RB setupmessage at step 1 k-05 (RRC message, e.g., 1 e-10, 1 e-20, or 1 e-35 ofFIG. 1E). The terminal may identify respective conditions (at step 1k-10). If a first condition and a second condition are satisfied, asecond method is applied (at step 1 k-15), and if the first conditionand a third condition are satisfied, a second method is applied (at step1 k-20). If a fourth condition is satisfied, a third method is applied(at step 1 k-25), and if a fifth condition is satisfied, a fourth methodis applied (at step 1 k-30). If a sixth condition is satisfied, a fifthmethod is applied (at step 1 k-35), and if a seventh condition issatisfied, a sixth method is applied (at step 1 k-40). If an eighthcondition is satisfied, a seventh method is applied (at step 1 k-45),and if a ninth condition is satisfied, an eighth method is applied (atstep 1 k-50).

FIG. 1L is a diagram of a terminal, according to an embodiment of thepresent disclosure.

The terminal includes a radio frequency (RF) processor 1 l-10, abaseband processor 1 l-20, a storage unit 1 l-30, and a controller 1l-40.

The RF processor 1 l-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. The RF processor 1 l-10 performs up-conversion of abaseband signal provided from the baseband processor 1 l-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 1 l-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a digital-to-analog converter (DAC), and ananalog-to-digital converter (ADC). Although only one antenna isillustrated in the drawing, the terminal may be provided with aplurality of antennas. The RF processor 1 l-10 may include a pluralityof RF chains. The RF processor 1 l-10 may perform beamforming, and forthe beamforming, the RF processor 1 l-10 may adjust phases and sizes ofsignals transmitted or received through the plurality of antennas orantenna elements. The RF processor may perform MIMO, and may receiveseveral layers during performing of a MIMO operation. The RF processor 1l-10 may perform reception beam sweeping through proper configuration ofthe plurality of antennas or antenna elements under the control of thecontroller, or may control the direction and the beam width of thereception beam so that the reception beam is synchronized with thetransmission beam.

The baseband processor 1 l-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the system. For example, during data transmission, the basebandprocessor 1 l-20 generates complex symbols by encoding and modulating atransmitted bit string. During data reception, the baseband processor 1l-20 restores a received bit string by demodulating and decoding thebaseband signal provided from the RF processor 1 l-10. When following anOFDM method, during data transmission, the baseband processor 1 l-20generates complex symbols by encoding and modulating a transmitted bitstring, performs mapping of the complex symbols on subcarriers, and thenconfigures OFDM symbols through the inverse fast Fourier transform(IFFT) operation and cyclic prefix (CP) insertion. During datareception, the baseband processor 1 l-20 divides the baseband signalprovided from the RF processor 1 l-10 in the unit of OFDM symbols,restores the signals mapped on the subcarriers through the fast Fouriertransform (FFT) operation, and then restores the received bit stringthrough demodulation and decoding.

The baseband processor 1 l-20 and the RF processor 1 l-10 transmit andreceive the signals as described above. Accordingly, the basebandprocessor 1 l-20 and the RF processor 1 l-10 may be called atransmitter, a receiver, a transceiver, or a communication unit. Inorder to support different radio connection technologies, at least oneof the baseband processor 1 l-20 and the RF processor 1 l-10 may includea plurality of communication modules. In order to process signals ofdifferent frequency bands, at least one of the baseband processor 1 l-20and the RF processor 1 l-10 may include different communication modules.The different radio connection technologies may include an LTE networkand an NR network. Further, the different frequency bands may includesuper high frequency (SHF) (e.g., 2.5 GHz or 5 GHz) band and millimeterwave (mmWave) (e.g., 60 GHz) band.

The storage unit 1 l-30 stores a basic program for an operation of theterminal, application programs, and data of setup information. Thestorage unit 1 l-30 provides stored data in accordance with a requestfrom the controller 1 l-40.

The controller 1 l-40 controls the terminal. The controller 1 l-40transmits and receives signals through the baseband processor 1 l-20 andthe RF processor 1 l-10. The controller 1 l-40 records or reads data inor from the storage unit 1 l-30. The controller 1 l-40 may include atleast one processor, and may include a communication processor forcommunication and an AP for controlling an upper layer, such as anapplication program.

FIG. 1M is a diagram of a base station in a wireless communicationsystem, according to an embodiment of the present disclosure.

The base station includes an RF processor 1 m-10, a baseband processor 1m-20, a backhaul communication unit (communication unit) 1 m-30, astorage unit 1 m-40, and a controller 1 m-50.

The RF processor 1 m-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. That is, the RF processor 1 m-10 performs up-conversionof a baseband signal provided from the baseband processor 1 m-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 1 m-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, and an ADC. Although only one antenna is illustratedin the drawing, the first connection node may be provided with aplurality of antennas. The RF processor 1 m-10 may include a pluralityof RF chains. The RF processor 1 m-10 may perform beamforming, and forthe beamforming, the RF processor 1 m-10 may adjust phases and sizes ofsignals transmitted or received through the plurality of antennas orantenna elements. The RF processor may perform down MIMO operationthrough transmission of one or more layers.

The baseband processor 1 m-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the first radio connection technology. During data transmission, thebaseband processor 1 m-20 generates complex symbols by encoding andmodulating a transmitted bit string. During data reception, the basebandprocessor 1 m-20 restores a received bit string by demodulating anddecoding the baseband signal provided from the RF processor 1 m-10. Whenfollowing an OFDM method, during data transmission, the basebandprocessor 1 m-20 generates complex symbols by encoding and modulating atransmitted bit string, performs mapping of the complex symbols onsubcarriers, and then configures OFDM symbols through the IFFT operationand CP insertion. During data reception, the baseband processor 1 m-20divides the baseband signal provided from the RF processor 1 m-10 in theunit of OFDM symbols, restores the signals mapped on the subcarriersthrough the FFT operation, and then restores the received bit stringthrough demodulation and decoding. The baseband processor 1 m-20 and theRF processor 1 m-10 transmit and receive the signals as described above.Accordingly, the baseband processor 1 m-20 and the RF processor 1 m-10may be called a transmitter, a receiver, a transceiver, or a wirelesscommunication unit.

The communication unit 1 m-30 provides an interface for performingcommunication with other nodes in the network.

The storage unit 1 m-40 stores a basic program for an operation of themain base station, application programs, and data of setup information.In particular, the storage unit 1 m-40 may store information on a bearerallocated to the connected terminal and the measurement result reportedfrom the connected terminal. The storage unit 1 m-40 may storeinformation that becomes a basis of determination whether to provide orsuspend a multi-connection to the terminal. The storage unit 1 m-40provides stored data in accordance with a request from the controller 1m-50.

The controller 1 m-50 controls the main base station. The controller 1m-50 transmits and receives signals through the baseband processor 1m-20 and the RF processor 1 m-10 or through the backhaul communicationunit 1 m-30. The controller 1 m-50 records or reads data in or from thestorage unit 1 m-40. For this, the controller 1 m-50 may include atleast one processor.

Embodiment 2

FIG. 2A is a diagram of an LTE system, according to an embodiment of thepresent disclosure.

Referring to FIG. 2A, as illustrated, a RAN of an LTE system includesENBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20, an MME 2 a-25, and an S-GW 2a-30. “UE 2 a-35 accesses to an external network through the ENBs 2a-05, 2 a-10, 2 a-15, and 2 a-20 and the S-GW 2 a-30.

In FIG. 2A, the ENB 2 a-05, 2 a-10, 2 a-15, and 2 a-20 correspond to anexisting node B of a UMTS system. The ENBs 2 a-05, 2 a-10, 2 a-15, or 2a-20 are connected to the UE 2 a-35 on a radio channel, and plays a morecomplicated role than that of the existing node B. In the LTE system,since all user traffics including a real-time service, such as a VoIPthrough an internet protocol, are serviced on shared channels, devicesperforming scheduling through consolidation of state information, suchas a buffer state, an available transmission power state, and a channelstate of each UE, are necessary, and the ENBs 2 a-05, 2 a-10, 2 a-15,and 2 a-20 correspond to such scheduling devices. In general, one ENBcontrols a plurality of cells. In order to implement a transmissionspeed of 100 Mbps, the LTE system uses, OFDM in a bandwidth of 20 MHz asa RAT. Further, the LTE system adopts an AMC scheme that determines amodulation scheme and a channel coding rate to match the channel stateof the terminal. The S-GW 2 a-30 provides a data bearer, and generatesor removes the data bearer under the control of the MME 2 a-25. The MME2 a-25 takes charge of not only mobility management of the UE 2 a-35 butalso various kinds of control functions, and is connected to theplurality of ENBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20.

FIG. 2B is a diagram of a radio protocol structure in an LTE system,according to an embodiment of the present disclosure.

Referring to FIG. 2B, in a UE or an ENB, a radio protocol of an LTEsystem includes a PDCP 2 b-05 or 2 b-40, an RLC 2 b-10 or 2 b-35, and aMAC 2 b-15 or 2 b-30. The PDCP 2 b-05 or 2 b-40 takes charge of IPheader compression/decompression operations. The main functions of thePDCP are summarized as follows:

-   -   Header compression and decompression: ROHC only;    -   Transfer of user data;    -   In-sequence delivery of upper layer PDUs at a PDCP        reestablishment procedure for an RLC AM;    -   For split bearers in DC (only support for an RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception;    -   Duplicate detection of lower layer SDUs at a PDCP        reestablishment procedure for an RLC AM;    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at a PDCP data-recovery procedure, for an        RLC AM;    -   Ciphering and deciphering; and    -   Timer-based SDU discard in an uplink.

The RLC 2 b-10 or 2 b-35 reconfigures a PDCP PDU with a proper size andperforms an ARQ operation and the like. The main functions of the RLC 2b-10 or 2 b-35 are summarized as follows.

-   -   Transfer of upper layer PDUs;    -   Error correction through an ARQ (only for AM data transfer);    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer);    -   Re-segmentation of RLC data PDUs (only for UM and AM data        transfer);    -   Reordering of RLC data PDUs (only for UM and AM data transfer);    -   Duplicate detection (only for UM and AM data transfer);    -   Protocol error detection (only for AM data transfer);    -   RLC SDU discard (only for UM and AM transfer); and    -   RLC reestablishment.

The MAC 2 b-15 or 2 b-30 is connected to several RLC layer devicesconfigured in one terminal, and performs multiplexing/demultiplexing ofRLC PDUs into/from MAC PDU. The main functions of the MAC2 b-15 or 2b-30 are summarized as follows;

-   -   Mapping between logical channels and transport channels;    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from TB transferred to/from the        physical layer on transport channels;    -   Scheduling information reporting;    -   HARQ function (error correction through HARQ);    -   Priority handling between logical channels of one UE;    -   Priority handling between UEs by means of dynamic scheduling;    -   MBMS service identification;    -   Transport format selection; and    -   padding.

The physical layer 2 b-20 or 2 b-25 performs channel coding andmodulation of upper layer data to configure and transmit OFDM symbols ona radio channel, or performs demodulation and channel decoding of theOFDM symbols received on the radio channel to transfer the demodulatedand channel-decoded symbols to an upper layer.

FIG. 2C is a diagram of a next-generation mobile communication system,according to an embodiment of the present disclosure.

Referring to FIG. 2C, a RAN of a next-generation mobile communicationsystem includes an NR gNB 2 c-10 and an NR CN 2 c-05. An NR UE 2 c-15accesses to an external network through the NR gNB 2 c-10 and the NR CN2 c-05.

The NR gNB 2 c-10 corresponds to an ENB of the existing LTE system. TheNR gNB 2 c-10 is connected to the NR UE 2 c-15 on a radio channel, and,thus, it can provide a more superior service than the service of theexisting node B. Since all user traffics are serviced on shared channelsin the next-generation mobile communication system, a device thatperforms scheduling through consolidation of status information, such asa buffer state of UEs 2 c-15, an available transmission power state, anda channel state, is required, and the NR NB 2 c-10 takes charge of this.One NR gNB generally controls a plurality of cells. In order toimplement ultrahigh-speed data transmission as compared with theexisting LTE, the NR gNB may have a bandwidth that is equal to or higherthan the existing maximum bandwidth, and a beamforming technology may beadditionally grafted in consideration of OFDM as an RAT. An AMC schemedetermining a modulation scheme and a channel coding rate to match thechannel state of the UE 2 c-15 is adopted. The NR CN 2 c-05 performsmobility support, bearer setup, and QoS configuration. The NR CN 2 c-05is a device that takes charge of not only a mobility management functionof the UE 2 c-15 but also various kinds of control functions, and isconnected to a plurality of ENBs. Further, the next-generation mobilecommunication system may interlock with the existing LTE system, and theNR CN 2 c-05 is connected to an MME 2 c-25 through a network interface.The MME 2 c-25 is connected to an ENB 2 c-30 that is the existing ENB.

FIG. 2D is a diagram of a radio protocol structure of a next-generationmobile communication system, according to an embodiment of the presentdisclosure.

In a UE or an NR ENB, a radio protocol of the next-generation mobilecommunication system includes an NR PDCP 2 d-05 or 2 d-40, an NR RLC 2d-10 or 2 d-35, and an NR MAC 2 d-15 or 2 d-30. The main functions ofthe NR PDCP 2 d-05 or 2 d-40 may include parts of the followingfunctions:

-   -   Header compression and decompression: ROHC only;    -   Transfer of user data;    -   In-sequence delivery of upper layer PDUs;    -   PDCP PDU reordering for reception;    -   Duplicate detection of lower layer SDUs;    -   Retransmission of PDCP SDUs;    -   Ciphering and deciphering; and    -   Timer-based SDU discard in an uplink.

As described above, reordering of the NR PDCP devices may includereordering of PDCP PDUs received from a lower layer based on PDCP SNs.The reordering may include transfer of data to an upper layer in theorder of reordering, recording of lost PDCP PDUs through reordering,status report for the lost PDCP PDUs to a transmission side, andretransmission request for the lost PDCP PDUs.

The main functions of the NR RLC 2 d-10 or 2 d-35 may include parts ofthe following functions:

-   -   Transfer of upper layer PDUs;    -   In-sequence delivery of upper layer PDUs;    -   Out-of-sequence delivery of upper layer PDUs;    -   Error correction through an ARQ;    -   Concatenation, segmentation, and reassembly of RLC SDUs;    -   Re-segmentation of RLC data PDUs;    -   Reordering of RLC data PDUs;    -   Duplicate detection;    -   Protocol error detection;    -   RLC SDU discard; and    -   RLC reestablishment.

As described above, in-sequence delivery of NR RLC devices may includein-sequence delivery of RLC SDUs received from a lower layer to an upperlayer. When one original RLC SDU is segmented into several RLC SDUs tobe received, the delivery may include reassembly and delivery of the RLCSDUs, reordering of the received RLC PDUs based on an RLC SN or a PDCPSN, recording of lost RLC PDUs through reordering, status report for thelost RLC PDUs to a transmission side, retransmission request for thelost PDCP PDUs, in-sequence delivery of only RLC SDUs just before thelost RLC SDU to an upper layer if there is the lost RLC SDU, in-sequencedelivery of all RLC SDUs received before a specific timer starts itsoperation to an upper layer if the timer has expired although there isthe lost RLC SDU, or in-sequence delivery of all RLC SDUs received up tonow to an upper layer if the timer has expired although there is thelost RLC SDU. As described above, the RLC PDUs may be processed in theorder of their reception (regardless of the order of the SNs, in theorder of their arrival), and may be transferred to the PDCP device in anout-of-sequence manner. In a case of segments, such segments stored inthe buffer or to be received later may be received and reconfigured toone complete RLC PDU, and then may be transferred to the PDCP device.The NR RLC layer may not include a concatenation function, and thefunction may be performed by an NR MAC layer or may be replaced by amultiplexing function of the NR MAC layer.

The out-of-sequence delivery of the NR RLC device 2 d-10 includes afunction of transferring the RLC SDUs received from a lower layerdirectly to an upper layer in an out-of-sequence manner. If one originalRLC SDU is segmented into several RLC SDUs to be received, the deliverymay include reassembly and delivery of the RLC SDUs, and recording ofthe lost RLC PDUs through storing and ordering the RLC SNs or PDCP SNsof the received RLC PDUs.

The NR MAC 2 d-15 or 2 d-30 may be connected to several NR RLC layerdevices configured in one UE, and the main functions of the NR MAC mayinclude parts of the following functions:

-   -   Mapping between logical channels and transport channels;    -   Multiplexing/demultiplexing of MAC SDUs;    -   Scheduling information reporting;    -   HARQ function (error correction through HARQ);    -   Priority handling between logical channels of one UE;    -   Priority handling between UEs by means of dynamic scheduling;    -   MBMS service identification;    -   Transport format selection; and    -   padding.

The NR PHY layer 2 d-20 or 2 d-25 may perform channel coding andmodulation of upper layer data to configure and transmit OFDM symbols toa radio channel, or may perform demodulation and channel decoding of theOFDM symbols received on the radio channel to transfer the demodulatedand channel-decoded symbols to an upper layer.

FIG. 2E is a diagram of modes in which a terminal can stay in anext-generation mobile communication system, according to an embodimentof the present disclosure.

A terminal (UE) may stay in an RRC connected mode 2 e-03, an RRCinactive mode 2 e-02 (or a lightly-connected mode 2 e-02), and an RRCidle mode 2 e-01, and may pass through processes of switching over todifferent modes 2 e-05, 2 e-10, 2 e-15, 2 e-20, and 2 e-25. That is, theUE in the RRC idle mode 2 e-01 may be switched to the RRC connected mode2 e-03 (via 2 e-05) to transmit/receive data if data to be transmittedto an uplink is generated, if a paging message is received througharrival of downlink data, or if an access to the network is configuredto update a tracking area.

If data is not generated for a predetermined time after the data istransmitted or received, the UE in the RRC connected mode 2 e-03 may beswitched to the RRC idle mode 2 e-01 by the network (via 2 e-15).Further, if data is not generated for a predetermined time, the UE inthe RRC connected mode 2 e-03 may be switched to the RRC inactive mode 2e-02 by the network or by itself for the purpose of battery saving andrapid access support (via 2 e-20).

If data to be transmitted to an uplink is generated, if a paging messageis received through arrival of downlink data, or if an access to thenetwork is configured to update a tracking area (or RAN notificationarea) (periodically or if the UE deviates from the tracking area (or RANnotification area), the UE in the RRC inactive mode 2 e-02 may beswitched to the RRC connected mode 2 e-03 (via 2 e-10). The UE in theRRC inactive mode 2 e-02 may be shifted to the RRC idle mode 2 e-01 byindication of the network, by pre-engaged configuration, or by itself(via 2 e-25).

If many UEs in the RRC inactive mode exist in the network, this maycause signaling overhead of the network to be increased due to frequentprocedures of updating a RAN notification area, and, thus, shifting ofthe UEs in the RRC inactive mode to the RRC idle mode should besupported. When the UE has a specific purpose, it may transmit data evenin the RRC inactive mode 2 e-02 without being shifted to the RRCconnected mode 2 e-03, repeat shifting in accordance with the indicationof the network between the RRC inactive mode 2 e-02 and the RRC idlemode 2 e-01, and may proceed to be shifted to the RRC connected modeonly in case of need.

In the above-described procedure, since the UE in the RRC inactive modetransmits data in the RRC inactive mode, it has the advantages that ithas a very short transmission delay and very small signaling overhead.When transmitting only a small amount of data, the UE may correspond tothe UE transmitting data intermittently or for a very long period. TheUE in the RRC idle mode 2 e-01 may be directly shifted to the RRCinactive mode 2 e-02 by the network, or may be shifted to the RRCconnected mode 2 e-03 and then may be shifted to the RRC inactive mode 2e-02 (via 2 e-20).

In order to solve the state mismatch problem between the mode of the UEthat performs shifting between the modes and the mode of the UE that isrecognized by the network, an inactive timer may be additionallyconfigured to be driven in the UE. Further, such an inactive timer mayalso be driven in the ENB.

The RRC inactive mode and the lightly-connected mode may be analyzed asthe same state modes, and it may be assumed that the UE performs thesame operation. The RRC inactive mode and the lightly-connected mode maybe analyzed as the same state modes, but it may be assumed that the UEperforms different operations in the respective modes. The RRC inactivemode and the lightly-connected mode may be analyzed as different statemodes, and it may be assumed that the UE performs different operationsin the respective modes. Although the RRC inactive mode and thelightly-connected mode have the same purpose on the point that a rapidre-access becomes possible with small signaling and the battery can besaved, they may be the same modes or different modes depending onimplementation of the UE and the network and their definition. The UEoperation in the RRC inactive mode and the lightly-connected mode may bethe same as the operation in the RRC idle mode, may have an additionalfunction, or may have only a partial function of the operation in theRRC idle mode.

As described above, in the RRC inactive mode, a UE battery can be saved,and when the UE accesses to the network, a rapid access can beconfigured with a small signaling overhead. However, the UE in the RRCinactive mode should perform a procedure for updating a RAN notificationarea more frequently than a procedure in which the UE in the RRC idlemode periodically updates a tracking area. Accordingly, if many UEs inthe RRC inactive mode exist in the network, this may cause the signalingoverhead due to the procedure for periodically updating the periodic RANnotification area, and, thus, it is necessary for the network to managethe UEs in the RRC inactive mode and, if needed, to switch the UEs inthe RRC inactive mode to the RRC idle mode.

FIG. 2F is a flowchart of a method for a terminal switched from an RRCconnected mode to an RRC idle mode and a terminal switched from the RRCidle mode to the RRC connected mode, according to an embodiment of thepresent disclosure.

Referring to FIG. 2F, if a terminal (UE) transmitting/receiving data inthe RRC connected mode does not transmit/receive the data for a specificcause/reason or for a predetermined time, an ENB may transmit anRRCConnectionRelease message to the UE causing the UE to be switched tothe RRC idle mode (at step 2 f-01). Thereafter, if data to betransmitted is generated, the UE (“idle mode UE”), of which connectionis not currently set, performs an RRC connection establishment processwith the ENB. The UE establishes backward transfer synchronization withthe ENB through a random access procedure, and transmits anRRCConnectionRequest message to the ENB (at step 2 f-05). The messagecontains an identifier of the UE and a connection establishment cause.The ENB transmits an RRCConnectionSetup message to the UE so that the UEsets the RRC connection (at step 2 f-10). The message may contain RRCconnection setup information and etc. The RRC connection is also calledan SRB, and is used to transmit/receive an RRC message that is a controlmessage between the UE and the ENB.

The UE having set the RRC connection transmits anRRCConnectionSetupComplete message to the ENB (at step 2 f-15). Themessage contains a control message SERVICE REQUEST for the UE to requesta bearer setup for a specific service from an MME. The ENB transmits theSERVICE REQUEST message contained in the RRCConnectionSetupCompletemessage to the MME (at step 2 f-20), and the MME determines whether toprovide the service requested by the UE. If it is determined to providethe service requested by the UE as the result of the determination, theMME transmits an INITIAL CONTEXT SETUP REQUEST message to the ENB (atstep 2 f-25). The message includes QoS information to be applied duringDRB setup and security related information (e.g., security key orsecurity algorithm) to be applied to the ERB. In order to set thesecurity with the UE, the ENB exchanges a SecurityModeCommand message atstep 2 f-30 and a SecurityModeComplete message at step 2 f-35 with theUE. If the security setup is completed, the ENB transmits anRRCConnectionReconfiguration message to the UE (at step 2 f-40). Themessage includes setup information of the DRB whereby user data is to beprocessed, and the UE sets the DRB by applying the information, andtransmits an RRCConnectionReconfigurationComplete message to the ENB (atstep 2 f-45).

The ENB that has completed the DRB setup with the UE transmits anINITIAL CONTEXT SETUP COMPLETE message to the MME (at step 2 f-50), andthe MME that has received this exchanges an S BEARER SETUP message andan S BEARER SETUP RESPONSE message with an S-GW in order to set the Sbearer (at steps 2 f-055 and 2 f-60). The S1 bearer is a connection fortransmitting data set between the S-GW and the ENB, and corresponds tothe DRB in a one-to-one manner. If the above-described steps arecompleted, the terminal transmits/receives data to/from the ENB throughthe S-GW (at steps 2 f-65 and 2 f-70). As described above, a generaldata transmission process is briefly composed of three stages of RRCconnection setup, security setup, and DRB setup. Further, the ENB maytransmit the RRCConnectionReconfiguration message to the UE in order torenew, add, or change the setup for a specific cause (at step 2 f-75).

As described above, in order to switch from the RRC idle mode to the RRCconnected mode, many signaling procedures are required. Accordingly, inthe next-generation mobile communication system, the RRC inactive modeor the lightly-connected mode may be newly defined, and in such a newmode, the UE and the ENB store a UE context. If needed, the S1 bearercan be maintained, and, thus, the access can be made more rapidly with asmall number of signaling procedures.

FIG. 2G is a flowchart of a method a terminal switched from an RRCconnected mode to an RRC inactive mode or a lightly-connected mode and aterminal switched from the RRC inactive mode or the lightly-connectedmode to the RRC connected mode, according to an embodiment of thepresent disclosure.

An overall flow among a UE 2 g-01, an anchor eNB 2 g-02, a new eNB 2g-03, and an MME 2 g-04 in order to perform a procedure of reusing a UEcontext and an S1 bearer between a UE and an eNB. The UE 2 g-01 in anRRC connection state transmits/receives data to/from the eNB 2 g-02. Ifthe data transmission/reception is interrupted, the eNB 2 g-02 operatesa specific timer, and if the data transmission/reception is not resumeduntil the timer expires (at step 2 g-05), the eNB 2 g-02 considersrelease of the RRC connection of the UE 2 g-01. At step 2 g-10, in orderto shift the UE 2 g-01 to an RRC inactive state or a light connectedstate, the eNB 2 g-02 may transmit an RRCConnectionSuspend message, anewly defined RRC message, or another existing reused RRC messageinstead of an RRCConnectionRelease message. At step 2 g-10, the eNB 2g-02 may store a UE context after releasing the RRC connection of the UE2 g-01 in accordance with a specific rule, may allocate a resume IDwhile transmitting a control message indicating to release the RRCconnection to the UE 2 g-01, and may configure a paging area (PA) inwhich the UE 2 g-01 is to report mobility during the light connectedmode. In this case, through the resume ID allocation, the UE 2 g-01stores the UE context, or the eNB 2 g-02 may include a separate contextmaintenance indication for indicating that the UE 2 g-01 operates in thelight connected mode and the UE context is stored in the message to betransmitted (at step 2 g-10). The message may include securityinformation for updating the security setup that is necessary when theUE 2 g-01 performs an RRC connection resume procedure. For example, aNextHopChainingCount (NCC) may be pre-allocated, and using this, a newsecurity key KeNB may be calculated and configured. The control messagemay include a list of cells to which a procedure of using the storedcontext can be applied in a period in which the eNB 2 g-02 maintains thecontext or when the UE 2 g-01 intends to reconfigure the RRC connectionin an effective period.

After releasing the RRC connection of the UE 2 g-01, the eNB 2 g-02maintains the UE context of the UE 2 g-01 and the S1 bearer as they are(at step 2 g-15). The S1 bearer calls an S-control bearer used totransmit/receive a control message between the eNB 2 g-02 and the MME 2g-04 and an S1-user plane bearer used to transmit/receive user databetween the eNB 2 g-02 and the S-GW. By maintaining the S1 bearer, aprocedure for S1 bearer setup can be omitted when the UE 2 g-01 intendsto set the RRC connection in the same cell or in the same eNB 2 g-02. Ifthe effective period expires, the eNB 2 g-02 may delete the UE contextand may release the S1 bearer. The UE 2 g-01 that has received theRRCConnectionRelease message at step 2 g-10 switches to the lightconnected mode.

The eNB 2 g-02 transmits a control message for requesting a connectionsuspend from the MME 2 g-04 (at step 2 g-20). If downlink data for theUE 2 g-01 is generated, the MME 2 g-04 that has received the controlmessage may instruct the S-GW to request the MME 2 g-04 to start apaging procedure without transferring the downlink data to the eNB 2g-02, and the S-GW may operate accordingly. If downlink data for the UE2 g-01 is generated, the S-GW may directly transfer the downlink data tothe eNB 2 g-02, and the eNB 2 g-02 may generate and transfer a pagingmessage to a neighboring eNB (at step 2 g-35). That is, the eNB 2 g-02that has received the downlink data stores the data in a buffer andproceeds with a paging procedure. The eNB 2 g-02 calls an eNB thatmaintains the UE context of the UE and an S1-U bearer.

The UE 2 g-01 that has received the RRCConnectionRelease message at step2 g-10 including information indicating context maintenance and a resumeID may release the RRC connection, but may operate the timercorresponding to an effective period, record an effective cell list in amemory, maintain the current UE context in the memory without deletingthe same (at step 2 g-25), and be shifted to the light connected mode.The UE context as described above includes various kinds of informationrelated to the RRC setup of the UE 2 g-01, and includes SRB setupinformation, DRB setup information, and security key information.Thereafter, the RRC connection is set (at step 2 g-30). The UE 2 g-01 towhich the resume ID was not allocated in the previous RRC connectionrelease process or for which context maintenance has not been indicatedmay perform the general RRC connection setup process, as described abovewith reference to FIG. 2F, whereas the light-connected mode UE 2 g-01 towhich the resume ID was allocated in the previous RRC connection releaseprocess may attempt an RRC connection resume process using the stored UEcontext. The light-connected mode UE 2 g-01 may perform the general RRCconnection setup process (FIG. 2F) or may perform the RRC connectionresume process using the stored UE context depending on whether thelight connection of the network is supported.

Each eNB 2 g-02 or the new eNB 2 g-03 or each cell may include anindication indicating whether the eNB 2 g-02 or the new eNB 2 g-03 orthe cell supports the light connection in system information to betransmitted. The indication may be included in the second blockSysteminformation of the system information, and may be included inblocks Systeminformation of other system information. Support of thelight connection as described above may include the corresponding eNB orcorresponding cell that can set and support the steps 2 g-50, 2 g-55, 2g-60, 2 g-65, 2 g-70, 2 g-75, 2 g-80, 2 g-85, and 2 g-90. If RRCconnection needs to be set, the light-connected mode UE 2 g-01 acquiresthe system information of the cell that is currently in a camp-on state.If the system information does not include the indication indicatingthat the new eNB 2 g-03 or cell supports the light connection, the UE 2g-01 may perform the general RRC connection setup process as describedabove with reference to FIG. 2F (at step 2 g-45). However, if the systeminformation includes the indication indicating that the new eNB 2 g-03or cell supports the light connection, the UE 2 g-01 may perform the RRCconnection resume process using the stored UE context (at step 2 g-45).The RRC connection resume process using the stored UE context is asfollows.

First, the UE 2 g-01 transmits a preamble on message 1 in order toperform a random access procedure. If resource allocation is possible inaccordance with the preamble received on message 1, the new eNB 2 g-03allocates a corresponding uplink resource to the UE 2 g-01 on a message2. The UE 2 g-01 transmits a resume request message including a resumeID received at step 2 g-10 based on the received uplink resourceinformation (at step 2 g-50). The message may be a modified message ofthe RRCConnectionRequest message or a newly defined message (e.g.,RRCConnectionResumeRequest message). If the UE 2 g-01 that is in thelight-connected mode through connection release by the eNB 2 g-02 movesto be in the camp-on state in the cell of another eNB, the new eNB 2g-03 may know from what eNB the corresponding UE 2 g-01 previouslyreceived the service through reception and identification of the resumeID of the UE 2 g-01.

If the new eNB 2 g-03 has successfully received and identified theresume ID, it performs a context retrieve procedure for retrieving theUE context from the eNB 2 g-02 (at steps 2 g-55 and 2 g-60). If the UEcontext retrieve procedure has failed, for example, if an anchor/sourceeNB cannot be found or if the UE context does not exist, the new eNB 2g-03 may transmit the RRCConnectionSetup message of FIG. 2F instead ofthe RRCConnectionResume message, and may fall back on the RRC connectionsetup procedure of FIG. 2F instead of the subsequent bearer setupprocedure/security setup procedure. The new eNB 2 g-03 may bring the UEcontext from the eNB 2 g-02 through an S1 or X2 interface. When the neweNB has received the resume ID, but has not successfully discriminatedthe UE 2 g-01 for a specific cause, it may transmit theRRCConnectionSetup message to the UE 2 g-01 to fall back on the generalRRC connection setup procedure of FIG. 2F. That is, the eNB 2 g-02 maytransmit the RRCConnectionSetup message to the UE 2 g-01, and the UE 2g-01 that has received the RRCConnectionSetup message may transmit anRRCConnectionSetupComplete message to the new eNB 2 g-03 to perform theconnection setup. Further, if the new eNB 2 g-03 has received the resumeID, but has not successfully discriminated the UE 2 g-01 (e.g.,retrieval of the UE context from the eNB 2 g-02 has failed), it maytransmit an RRCConnectionRelease message or an RRCConnectionRejectmessage to the UE 2 g-01 to reject the connection of the UE 2 g-01, andmay again attempt to start the general RRC connection setup procedure ofFIG. 2F.

The new eNB 2 g-03 identifies MAC-I based on the retrieved UE context(at step 2 g-65). The MAC-I is a message authentication code calculatedby the UE 2 g-01 with respect to the control message through applicationof the security information of the restored UE context, that is, throughapplication of a security key and a security counter. The new eNB 2 g-03identifies integrity of the message using the MAC-I of the message andthe security key and the security counter stored in the UE context.Further, the new eNB 2 g-03 determines the setup to be applied to theRRC connection of the UE 2 g-01, and transmits the RRCConnectionResumemessage containing the setup information to the UE 2 g-01 (at step 2g-70). The new eNB 2 g-03 may identify the resume ID of the UE 2 g-01and may cipher the RRCConnectionResume message using a new security keyKeNB to transmit the ciphered RRCConnectionResume message, and the UE 2g-01 may normally receive the RRCConnectionResume message throughciphering of the RRCConnectionResume message using the new security keyKeNB calculated using the NCC pre-allocated at step 2 g-10. Aftertransmitting the RRCConnectionResume message, the RRC message and datamay be ciphered by the new security key, and may be transmitted andreceived by the UE 2 g-01 and the new eNB 2 g-03. TheRRCConnectionResume message may be a control message obtained byincluding information (REUSE INDICATOR) indicating RRC context reuse inthe general RRC connection request message. The RRCConnectionResumemessage includes various kinds of information related to the RRCconnection setup of the UE in the same manner as the RRCConnectionSetupmessage.

If the UE 2 g-01 receives the general RRCConnectionSetup message, itsets the RRC connection based on the setup information indicated in theRRCConnectionSetup message, whereas if the UE 2 g-01 receives theRRCConnectionResume message, it sets the RRC connection (deltaconfiguration) in consideration of both the stored setup information andthe setup information indicated in the control message. The UE 2 g-01may determine the setup information to be applied by determining theindicated setup information as delta information for the stored setupinformation, and may update the setup information or the UE context. IfSRB setup information is included in the RRCConnectionResume message,the UE 2 g-01 configures the SRB through application of the indicatedSRB setup information, whereas if the SRB setup information is notincluded in the RRCConnectionResume message, the UE configures the SRBthrough application of the SRB setup information stored in the UEcontext.

The UE 2 g-01 configures the RRC connection by applying the updated UEcontext and setup information, and transmit anRRCConnectionResumeComplete message to the new eNB 2 g-03 (at step 2g-75). Further, the new eNB 2 g-03 transmits a control message forrequesting a connection suspend release to the MME 2 g-04, and requeststhe MME 2 g-04 to reconfigure the S1 bearer to the new eNB 2 g-03 (atsteps 2 g-80 and 2 g-85). If the above-described message is received,the MME 2 g-04 requests the S-GW to reconfigure the S1 bearer to the neweNB 2 g-03, and indicates to normally process the data for the UE 2g-01. If the above-described process is completed, the UE 2 g-01 resumesdata transmission/reception in the cell of the new eNB 2 g-03 (at step 2g-90).

In the above-described procedure, if the existing anchor eNB 2 g-02releases the connection and the UE 2 g-01 that is in the light-connectedmode does not move greatly to be again in the camp-on state in the cellof the existing eNB 2 g-02, the eNB 2 g-02 may perform only theconnection suspend release of the S1 bearer instead of the procedures atsteps 2 g-80 and 2 g-85 without performing steps 2 g-55 and 2 g-60,search for the UE context of the UE 2 g-01 with reference to the resumeID indicated in message3, and based on this, reconfigure the connectionin a method similar to the above-described procedures.

If the data transmission/reception is interrupted, the new eNB 2 g-03operates a specific timer, and if the data transmission/reception is notresumed until the timer expires (at step 2 g-95), the new eNB 2 g-03considers release of the RRC connection of the UE 2 g-01. At step 2g-100, in order to shift the UE 2 g-01 to the RRC inactive state or thelight connected state, the eNB 2 g-02 may transmit anRRCConnectionSuspend message, a newly defined RRC message, or anotherexisting reused RRC message instead of the RRCConnectionRelease message.At step 2 g-100, the new eNB 2 g-03 may store the UE context afterreleasing the RRC connection of the UE 2 g-01 in accordance with aspecific rule, may allocate the resume ID while transmitting the controlmessage indicating to release the RRC connection to the UE 2 g-01, andmay configure a PA in which the UE 2 g-01 is to report mobility duringthe light-connected mode (at step 2 g-100). If the UE 2 g-01 in thelight-connected mode (at step 2 g-105) deviates from the configuredpaging area, it perform a paging area updating procedure.

FIG. 2H is a flowchart of a method for switching a terminal from an RRCconnected mode to an RRC inactive mode (or lightly-connected mode),according to an embodiment of the present disclosure.

Referring to FIG. 2H, it may be necessary for an eNB to shift the UE inan RRC connected mode (at step 2 h-05) to an RRC inactive mode e.g.,expiration of a specific timer. That is, data transmission/reception maynot be performed for a specific time. In order to shift the UE from theRRC connected mode to the RRC inactive mode, the eNB may transmit anRRCConnectionReconfiguration message (at step 2 h-10). The message maycontain information (or indication) for shifting the UE from the RRCconnected mode to the RRC inactive mode. If the message is received, theUE may transmit an RRCConnectionReconfigurationComplete message inresponse to the received message (at step 2 h-15), and may be switchedto the RRC inactive mode.

FIG. 2IA is a flowchart of a method for switching a terminal from an RRCinactive mode (or lightly-connected mode) to an RRC idle mode, accordingto the present disclosure.

Referring to FIG. 2IA, it may be necessary for an eNB to shift the UE inan RRC inactive mode (at step 2 ia-05) to an RRC idle mode, e.g.,expiration of a specific timer, or may be to reduce a signaling overheadof a network or to discard a UE context without storing the same anymore in the network. In order to shift the UE from the RRC inactive modeto the RRC idle mode, the eNB may first transmit a newly defined messageor a paging message for switching the mode to the UE (at step 2 ia-10).The message may be transmitted from an anchor eNB or a CN. If themessage is transmitted from the eNB, it may be featured to include a UEidentification (e.g., resume ID) capable of discriminating the UE in theRRC inactive mode, whereas if the message is transmitted from the CN, itmay be featured to include a system architecture evolution—temporarymobile subscriber identity S-TMSI or international mobile subscriberidentity (IMSI). If the message is transmitted from the eNB, the UE thathas received the message may transmit an RRCConnectionResumeRequestmessage to the eNB in response to the received message, whereas if themessage is transmitted from the CN, the UE may transmit anRRCConnectionRequest message (at step 2 ia-15). The eNB that hasreceived the message may transmit an RRCConnectionRelease message to theUE in order to shift the UE to an idle state (at step 2 ia-20). If themessage is received, the UE is switched to the RRC idle mode (at step 2ia-25).

If it is unable to directly switch the UE in the RRC inactive mode (atstep 2 ia-30) from the RRC inactive mode to the RRC idle mode in thenetwork, the eNB may identify the UE identification (resume ID) of theUE when the UE intends to perform the RRC connection resume setupprocedure (at step 2 ia-35), and may transmit the RRCConnectionReleasemessage at step 2 ia-40 in order to shift the UE to the RRC idle mode.The UE that has received the message is switched to the RRC idle mode(at step 2 ia-45).

FIG. 2IB is a flowchart of a method of a (2-1)-th embodiment forswitching a terminal from an RRC inactive mode (or lightly-connectedmode) to an RRC idle mode, according to the present disclosure.

Referring to FIG. 2IB, it may be necessary for an eNB to shift the UE inan RRC inactive mode (at step 2 ib-05) to an RRC idle mode, e.g., beexpiration of a specific timer, or may be to reduce a signaling overheadof a network or to discard a UE context without storing the same anymore in the network. In order to shift the UE from the RRC inactive modeto the RRC idle mode, the eNB may first transmit a newly defined messageor a paging message for switching the mode to the UE (at step 2 ib-10).The message may be transmitted from the eNB or a CN. If the message istransmitted from the eNB, it may be featured to include a UEidentification (e.g., resume ID) capable of discriminating the UE in theRRC inactive mode, whereas if the message is transmitted from the CN, itmay be featured to include S-TMSI or IMSI. If the message is transmittedfrom the eNB, the UE that has received the message may transmit anRRCConnectionResumeRequest message to the eNB in response to thereceived message, whereas if the message is transmitted from the CN, theUE may transmit an RRCConnectionRequest message, and may be once shiftedto the RRC connected mode (at step 2 ib-15). The eNB may receive themessage, and in order to switch the UE to the idle state, it maytransmit an RRCConnectionResume message to the UE so as to first switchthe UE to the RRC connected mode (at step 2 ib-20). If the UE that hasreceived the message is first shifted to the RRC connected mode (at step2 ib-25), and transmits an RRCConnectionResumeComplete message to theeNB (at step 2 ib-30). If the eNB receives the message, it transmits theRRCConnectionRelease message to the UE (at step 2 ib-35) to switch theUE to the RRC idle mode (at step 2 ib-40).

FIG. 2IC is a flowchart of a method of a (2-2)-th embodiment forswitching a terminal from an RRC inactive mode (or lightly-connectedmode) to an RRC idle mode, according to an embodiment of the presentdisclosure.

Referring to FIG. 2IC, it may be necessary for an eNB to shift the UE inan RRC inactive mode (at step 2 ic-05) to an RRC idle mode, e.g.,expiration of a specific timer, or may be to reduce a signaling overheadof a network or to discard a UE context without storing the same anymore in the network. In order to shift the UE from the RRC inactive modeto the RRC idle mode, the eNB may first transmit a newly defined messageor a paging message for switching the mode to the UE (at step 2 ic-10).The message may be transmitted from the eNB or a CN. If the message istransmitted from the eNB, it may be featured to include a UEidentification (e.g., resume ID) capable of discriminating the UE in theRRC inactive mode, whereas if the message is transmitted from the CN, itmay be featured to include S-TMSI or IMSI. If the message is transmittedfrom the eNB, the UE that has received the message may transmit anRRCConnectionResumeRequest message to the eNB in response to thereceived message (at step 2 ic-15). The eNB may receive the message, andin order to switch the UE to the idle state, it may transmit anRRCConnectionReject message to the UE in order to first switch the UE tothe idle state (at step 2 ic-20). The message may include an indicationindicating whether the UE continuously maintains the RRC inactive modeor suspends the RRC inactive mode and is shifted to the RRC idle state.If the message is received, the UE is switched to the RRC idle mode (atstep 2 ic-25).

FIG. 2ID is a flowchart of a method of a (2-3)-th embodiment forswitching a terminal from an RRC inactive mode (or lightly-connectedmode) to an RRC idle mode, according to the present disclosure.

Referring to FIG. 2ID, it may be necessary for an eNB to shift the UE inan RRC inactive mode (at step 2 id-05) to an RRC idle mode for aspecific cause. The specific cause may be expiration of a specifictimer, or may be to reduce a signaling overhead of a network or todiscard a UE context without storing the same any more in the network.In order to shift the UE from the RRC inactive mode to the RRC idlemode, the eNB may first transmit a newly defined message or a pagingmessage for switching the mode to the UE (at step 2 id-10). The messagemay be transmitted from an anchor eNB or a CN. If the message istransmitted from the eNB, it may be featured to include a UEidentification (e.g., resume ID) capable of discriminating the UE in theRRC inactive mode, whereas if the message is transmitted from the CN, itmay be featured to include S-TMSI or IMSI. Further, the messages may befeatured to include an indication indicating that the UE mode is to beshifted from the RRC inactive mode to the RRC idle mode. If theindication indicating that the UE mode is to be shifted to the RRC idlemode is included in the messages, the UE that has received the messagemay be shifted to the RRC idle mode state (at step 2 id-15). If thepaging message is transmitted from the eNB, the UE may transmit anRRCConnectionResumeRequest message to the eNB in response to the pagingmessage, whereas if the paging message is transmitted from the CN, theUE may transmit an RRCConnectionRequest message (at step 2 id-20). Inorder to reduce the signaling overhead as described above, the procedureat step 2 id-20 may be omitted.

When a UE is switched from an RRC inactive mode to an RRC idle mode,before being switched to the RRC inactive mode, the UE may select apublic land mobile network (PLMN) through cell selection. Whenperforming cell reselection in the selected PLMN, that is, if the UE isin a camped normally state (to search for a suitable cell), the UEmaintains the RRC inactive mode, and if the UE goes to an any cellselection state (to search for an acceptable cell or to reselect thePLMN), the UE may be automatically switched to the RRC idle mode.

Methods for efficiently switching a UE mode based on a timer are nowherein described. Prior to description of the above-described methods, aDRX of a UE will be first described.

FIG. 2J is a diagram of a DRX operation of the terminal, according to anembodiment of the present disclosure.

The DRX is applied to minimize power consumption of a UE, and is amonitoring technology only in a predetermined physical downlink controlchannel (PDCCH) in order to obtain scheduling information. The DRXoperation can be performed in both an RRC idle mode and an RRC connectedmode, and which are somewhat different from each other. In the RRC idlemode, the UE identifies existence/nonexistence of paging from an eNBthrough calculation of when the UE is awaken in a specific method. Thatis, the UE calculates a paging occasion, and goes back to an activestate to identify a signal from the eNB whenever the paging occasionbecomes possible. If there is no signal from the eNB, the UE goes backto the idle state again. The DRX operation of the UE in the RRCconnected mode is as follows. If the UE continuously monitors a PDCCH toacquire the scheduling information, it may cause great powerconsumption. The basic DRX operation has a DRX period at 2 j-00, and thePDCCH is monitored only for an on-duration time at 2 j-05. In theconnected mode, the DRX period is configured to have two values, e.g., along DRX and a short DRX. The long DRX period is applied, and if needed,the eNB may trigger the short DRX period using a MAC CE. After apredetermined time elapses, the UE is changed from the short DRX periodto the long DRX period. Initial scheduling information of a specific UEis provided only on the PDCCH. Accordingly, the UE periodically monitorsonly the PDCCH, and, thus, power consumption can be minimized.

If scheduling information on a new packet is received on the PDCCH forthe on-duration time at 2 j-05 (or at 2 j-10), the UE starts a DRXinactivity timer at 2 j-15. The UE maintains in an active state for theDRX inactivity timer. That is, the UE continues the PDCCH monitoring.The UE also starts an HARQ RTT timer at 2 j-20. The HARQ RTT timer isapplied to prevent the UE from unnecessarily monitoring the PDCCH forthe HARQ round trip time (RTT), and during the timer operating time, theUE is not required to perform the PDCCH monitoring. However, while thePRX inactivity timer and the HARQ RTT timer operate simultaneously, theUE continues the PDCCH monitoring based on the DRX inactivity timer. Ifthe HARQ RTT timer expires, a DRX retransmission timer at 2 j-25 starts.While the DRX retransmission timer operates, the UE should perform thePDCCH monitoring. In general, during the DRX retransmission timeroperating time, the scheduling information for the HARQ retransmissionis received (at 2 j-30). If the scheduling information is received, theUE immediately suspends the DRX retransmission timer, and starts theHARQ RTT timer again. The above-described operation continues until thepacket is successfully received (at 2 j-35).

Setup information related to the DRX operation in the RRC connected modeis transferred to the UE through the RRCConnectionReconfigurationmessage of FIG. 2F. The on-duration timer, the DRX inactivity timer, andthe DRX retransmission timer are defined by the number of PDCCHsubframes. If a predetermined number of subframes that are defined asPDCCH subframes have passed after the timer starts, the timer expires.In frequency-division duplexing (FDD), all downlink subframes belong toPDCCH subframes, and in time-division duplexing TDD, downlink subframesand special subframes correspond to them. In the TDD, downlinksubframes, uplink subframes, and special subframes exist in the samefrequency band. Among them, the downlink subframes and the specialsubframes are considered as the PDCCH subframes.

The eNB may configure two kinds of states longDRX and shortDRX. The eNBmay use one of two states in consideration of power preferenceindication information and UE mobility record information typicallyreported from the UE, and the characteristic of the configured DRB.Shifting between the two states is performed by transmitting whether aspecific timer has expired or a specific MAC CE to the UE. Further, ifneeded, the eNB may make the UE immediately bring the inactive timer toan end using the MAC CE.

FIG. 2K is a flowchart of a method of a third embodiment for switching aterminal from an RRC connected mode to an RRC inactive mode, accordingto an embodiment the present disclosure.

Referring to FIG. 2K, a case where an eNB does not configure a DRX to aUE is considered. In such a scenario, the eNB may configure a specifictimer value to the UE through an RRCConnectionSetup message or anRRCConnectionReconfiguration message in the previous RRC connectionestablishment at step 2 k-05. The specific timer value is used for atimer used for the UE to switch the modes. The UE in the RRC connectionmode (at step 2 k-10) may start the timer after a specific operation (atstep 2 k-15). The specific operation as described above may be anoperation in which the UE receives a signal from the eNB on the PDCCH ortransmits data to an uplink, or an operation in which the UE receivesdata. If the specific operation does not occur until the timer expires(at step 2 k-20), and the UE is switched to the RRC inactive mode (atstep 2 k-25). The eNB may determine whether the UE is switched to theRRC inactive mode by operating the timer in the same manner as the timerof the UE using the timer value configured by the eNB to the UE. Theabove-described procedure may be equally applied even when the UE isswitched from the RRC connected mode to the RRC idle mode.

FIG. 2L is a flowchart of a method of a fourth embodiment for switchinga terminal from an RRC inactive mode to an RRC idle mode, according toan embodiment of the present disclosure.

The eNB may configure a specific timer value to the UE through anRRCConnectionSetup message or an RRCConnectionReconfiguration message inthe previous RRC connection establishment at step 2 l-05. The specifictimer value is used for a timer used for the UE to switch the modes. TheUE in the RRC connection mode (at step 2 l-10) may start the timer aftera specific operation (at step 2 l-15). The specific operation asdescribed above may be an operation in which the UE receives a signalfrom the eNB on the PDCCH or transmits data to an uplink, an operationin which the UE receives data, or an operation in which the UE receivesa paging message. If the specific operation does not occur until thetimer expires (at step 2 l-20), and the UE is switched to the RRC idlemode (at step 2 l-25). The eNB may determine whether the UE is switchedto the RRC idle mode by operating the timer in the same manner as thetimer of the UE using the timer value configured by the eNB to the UE.

As described above, the eNB may configure one timer to the UE, and maymake the UE use the third embodiment and the fourth embodiment whenswitching the respective modes. Further, the eNB may configure twodifferent timers, and may make the UE use the third embodiment and thefourth embodiment when switching the respective modes.

FIG. 2M is a flowchart of a method of a fifth embodiment for switching aterminal from an RRC connected mode to an RRC inactive mode, accordingto an embodiment of the present disclosure.

When an eNB configures a DRX to a UE, the eNB may configure a specificvalue to the UE through an RRCConnectionSetup message or anRRCConnectionReconfiguration message in the previous RRC connectionestablishment at step 2 m-05 (e.g., steps 2 f-10, 2 f-40, or 2 f-75 ofFIG. 2F). The specific value is used for the UE to switch the modes. Thespecific value may represent the number of times of DRX periods, or maybe a DRX inactive timer value. The UE in the RRC connected mode (at step2 m-10) as described above may operate the DRX after transmitting orreceiving data. If the specific value is configured as the number N ofDRX periods to the UE in the previous RRC connection establishmentprocedure, the UE operates the DRX (at step 2 m-15), and if the specificoperation does not occur until the DRX period is completed N times (atstep 2 m-20), the UE is switched to the RRC inactive mode (at step 2m-25).

The specific value may be broadcasted from system information of eachcell, and if the above-described value is not configured by the RRCmessage, the specific value broadcasted from the system information maybe used as default. Thereafter, if the network configures a specificvalue to the UE through the RRC message (e.g.,RRCConnectionReconfiguration message), the default value may be updatedby the specific value. The specific operation as described above may bean operation in which the UE receives a signal from the eNB on the PDCCHor transmits data to an uplink or an operation in which the UE receivesdata.

The eNB may determine whether the UE is switched to the RRC inactivemode by checking the DRX operation in the same manner as that of the UEusing the specific value configured by the eNB to the UE. If thespecific value is configured as the DRX inactive timer value to the UEin the previous connection establishment procedure, the UE operates theDRX, and if the DRX inactive timer expires, the UE may be switched tothe RRC inactive mode. In the same manner, the eNB can know that the UEhas been switched to the RRC inactive mode in the next DRX period. Theabove-described procedure can be applied in the same manner even whenthe UE is switched from the RRC connected mode to the RRC idle mode.

FIG. 2N is a flowchart of a method of a sixth embodiment for switching aterminal from an RRC inactive mode to an RRC idle mode, according to anembodiment of the present disclosure.

In an RRC inactive mode, UE identifies existence/nonexistence of pagingfrom an eNB through calculation of when the UE is awaken in a specificmethod. That is, the UE calculates a paging occasion, and goes back toan active state to identify a signal from the eNB whenever the pagingoccasion becomes possible. If there is no signal from the eNB, the UEgoes back to the inactive state again. The eNB may configure a specificvalue to the UE through an RRCConnectionSetup message or anRRCConnectionReconfiguration message in the previous RRC connectionestablishment at step 2 n-05 (e.g., steps 2 f-10, 2 f-40, or 2 f-75 ofFIG. 2F). The specific value is used for the UE to switch the modes. Thespecific value may represent the number of times of DRX periods.

The specific value may be broadcasted from the system information ofeach cell, and if the above-described value is not configured by the RRCmessage, the specific value broadcasted from the system information maybe used as default. Thereafter, if the network configures a specificvalue to the UE through the RRC message (e.g.,RRCConnectionReconfiguration message), the default value may be updatedby the specific value. The DRX period means a period in which the pagingoccurs. The UE in the RRC connected mode (at step 2 n-10) may operatethe DRX after transmitting or receiving data. That is, it may berepeated that the UE calculates the paging, identifies the signal fromthe eNB in the active state only in case where the paging can occur, andgoes back to the inactive state again. Through calculation of thepaging, time measured from a time point when the paging can occur to atime point when the next paging can occur may be considered as oneperiod.

If the specific value is configured as the number N of DRX periods tothe UE in the previous RRC connection establishment procedure, the UEoperates the DRX (at step 2 n-15), and if the specific operation doesnot occur until the DRX period is completed N times (at step 2 n-20)(i.e., the paging occasion time arrives N times), the UE may be switchedto the RRC idle mode (at step 2 n-25). The specific operation asdescribed above may be an operation in which the UE receives a signalfrom the eNB on the PDCCH or transmits data to an uplink, or anoperation in which the UE receives a paging message. The eNB maydetermine whether the UE is switched to the RRC idle mode by checkingthe DRX operation in the same manner as that of the UE using thespecific value configured by the eNB to the UE.

The eNB may configure one specific value to the UE, and may make the UEuse the fifth embodiment and the sixth embodiment when switching therespective modes. Further, the eNB may configure two different specificvalues, and may make the UE use the fifth embodiment and the sixthembodiment when switching the respective modes.

In the third, fourth, fifth, and sixth embodiments, when the eNBtransmits a specific value to the UE through the RRCConnectionSetupmessage or the RRCConnectionReconfiguration message in the previous RRCconnection establishment, it may designate the specific mode to whichthe UE is to be switched. The specific mode may be configured to the RRCconnected mode, the RRC inactive mode, or the RRC idle mode.Accordingly, in the third, fourth, fifth, and sixth embodiments, if thespecific mode is configured together with the specific value in theprevious RRC connection establishment, the UE may be switched to thespecific mode in case where the operation corresponding to the specificvalue is satisfied in accordance with the respective operationsaccording to the third, fourth, fifth, and sixth embodiments. That is,it may be predetermined what mode the UE is to be switched to in theprevious RRC connection establishment within the same operationsaccording to the third, fourth, fifth, and sixth embodiments.

FIG. 2O is a diagram of a terminal, according to an embodiment of thepresent disclosure.

The UE may be switched from an RRC idle mode at 2 o-01 to an RRCconnected mode at 2 o-03 through the procedure as described above withreference to FIG. 2F (2 o-05). Further, the UE may be switched from theRRC connected mode at 2 o-03 to the RRC idle mode at 2 o-01 throughapplication of the procedure as described above with reference to FIG.2F (2 o-05) or the first, third, or fifth embodiment. The UE may beswitched from an RRC inactive mode at 2 o-02 to the RRC connected modeat 2 o-03 through the procedure as described above with reference toFIG. 2G (2 o-10), and may be switched from the RRC connected mode at 2o-03 to the RRC inactive mode at 2 o-02 through the procedure asdescribed above with reference to FIG. 2G (2 o-20) based on the first,third, or fifth embodiment. The UE may be switched from the RRC inactivemode at 2 o-02 to the RRC idle mode at 2 o-01 through the procedure asdescribed above with reference to FIG. 2G (2 o-25) based on the second,fourth, or sixth embodiment.

FIG. 2P is a flowchart of a method of a terminal in an RRC inactive modeat step 2 p-05 shifted to an RRC connected mode if downlink data isgenerated in a network, according to an embodiment of the presentdisclosure.

If downlink data for a certain UE is generated in the network, thenetwork may transmit a paging message at step 2 p-10 to the UE to notifythe UE that the UE is required to be shifted to the RRC connected mode.The paging message may be transmitted from a CN or an anchor eNB. Whenthe paging message transmitted from the CN, it may be featured toinclude an STMSI or an IMSI, whereas in case of the paging messagetransmitted from the anchor eNB, it may be featured to include a resumeID.

If the paging message includes the S-TMSI or IMSI when the UE receivesthe paging message, the UE may identify that the paging message has beentransmitted from the CN, and may perform a procedure of shifting from anRRC idle mode state as described above with reference to FIG. 2F to anRRC connected mode (at steps 2 f-05 to 2 f-75). If the paging messagereceived by the UE includes the resume ID, the UE may be shifted to theRRC connected mode in accordance with the RRC connection resumeprocedure as described above with reference to FIG. 2 g by performingthe steps 2 p-15, 2 p-20, 2 p-25, and 2 p-30. The step 2 p-30 may beomitted for the purpose of reducing the signaling overhead. FIG. 2Q is aflowchart of a method for accessing to a network in an RRC inactive moderejected by the network, according to an embodiment of the presentdisclosure.

Referring to FIG. 2Q, if uplink data occurs, if a tracking area or a RANnotification area is updated, or if a connection is set up for aspecific cause, the UE in the RRC inactive mode at step 2 q-05 maytransmit an RRCConnectionResumeRequest message to the eNB (at step 2q-10), and the eNB may transmit an RRCConnectionReject message to the UEfor the specific cause (at step 2 q-15). If the eNB desires that the UEis in the RRC inactive mode while maintaining the UE context in a statewhere transmission resources are insufficient or a big overhead occursin the network, the eNB may indicate this using the indication. The UEmay identify the indication of the eNB from the message (at step 2q-20), and may set a timer to the timer value included in the message.If the timer expires, as described above with reference to FIG. 2G, theUE may perform the RRC connection resume procedure again (at step 2q-25). However, if the UE context does not exist in the network or theRRC connection resume procedure is not supported any more, the eNB mayindicate this using the indication of the RRCConnectionReject message,and if the message is received, the UE may identify the indication, andmay not perform the RRC connection resume procedure. After the specifictimer expires, as described above with reference to FIG. 2F, the UE mayfall back on the RRC connection setup procedure (at step 2 q-30).

FIG. 2R is a flowchart of a method of a terminal in an RRC inactive modenot shifted to an RRC connected mode, but transmits uplink data in theRRC inactive mode, according to an embodiment of the present disclosure.

Referring to FIG. 2R, the UE in the RRC inactive mode has a UE context,and data to be transmitted to an uplink may be generated. The UE contextincludes bearer setup information, such as an SRB or a DRB, and may alsoinclude setup information for a logical channel and security setupinformation. The UE may include the same PDCP device setup informationas that used in the RRC connected state (e.g., PDCP COUNT value or PDCPsequence number). The UE may include the same RLC device setupinformation as that used in the RRC connected state. The UE in the RRCinactive mode may directly transmit uplink data through the network anda predetermined transmission resource without any random accessprocedure or connection setup procedure (at step 2 r-05). The data asdescribed above may include a UE identification (e.g., resume ID) sothat the network/eNB can discriminate the UE during transmission of thedata (at step 2 r-10). If the UE has data having a size that is largerthan the size of the pre-engaged transmission resource, the UE mayinclude a buffer status report (BSR) in the data to be transmitted inorder to be allocated with an additional transmission resource from theeNB. Further, the UE may include security setup information in the datato be transmitted.

If the data is received, the eNB identifies the identification of theUE, and transmits to the UE the UE identification together with an ACKnotifying of safe receipt of the message (at step 2 r-15). Thetransmission resource engaged between the UE and the network/eNB may notbe allocated to one UE but may be allocated to and shared by severalUEs. That is, the transmission resource may be occupied in acontention-based manner. Accordingly, the eNB may notify of contentionresolution through transmission of the UE identification together withthe ACK in the message. The message may include security setupinformation in the message to update the security setup of the UE. Asdescribed above, the ACK may be transmitted by an ARQ of an RLC device,an HARQ of a MAC device, the MAC CE, or the RRC message. That is, theACK and the UE identification may be transmitted in one of the fourmethods in accordance with the implementation and the prescribedengagement.

The above-described procedure in which the UE in the RRC inactive modeis not shifted to the RRC connected mode, but immediately transmits thedata may be determined by a specific threshold, or the eNB may make theUE immediately perform or not perform the procedure for immediatelytransmitting the data without the RRC connected mode shift procedureusing the specific identification. That is, when the data having anamount that is smaller than the specific threshold value, the data maybe directly transmitted without any procedure of shifting to the RRCconnected mode as described above, whereas when the data having anamount that is larger than the specific threshold value, the data may betransmitted by shifting to the RRC connected mode through performing ofthe RRC connection resume procedure as described above. The specificthreshold value or the identification may be set by the RRC connectionsetup message or the RRC connection reconfiguration message when the UEsets an initial connection as illustrated in FIG. 2G, or information onthe threshold value or the indication may be broadcasted from the systeminformation. The threshold value or the indication may be used asdefault, and the threshold value set by the eNB through the RRC message(or MAC CE) may be applied preferentially to the default value.

If the UE in the RRC inactive mode transmits the data in the RRCinactive mode without the procedure of shifting to the RRC connectedmode as described above, the battery power consumption of the UE can besaved, and the signaling overhead of the network can be reduced.

FIG. 2S is a flowchart of a method of a terminal in an RRC inactive modenot shifted to an RRC connected mode, but transmits uplink data in theRRC inactive mode, according to an embodiment of the present disclosure.

If uplink data is generated, a UE at step 2 s-05 in an RRC inactive modemay perform a random access procedure to set a connection to a network.Before transmitting the data in the RRC inactive mode, the UE may firsttransmit a preamble (at step 2 s-10). As the preamble, one of preamblegroups may be selected and transmitted. The preamble groups may bedivided into several sub-groups (partitions), and the respectivesub-groups may be divided in accordance with whether the UE intends totransmit a small amount of data in the RRC inactive mode, whether alarge amount of transmission resource is requested, or the requestedamount of transmission resource. That is, when the UE transmits thepreamble belonging to a specific sub-group, the eNB may identify anintention of the UE to transmit a small amount of data in the RRCinactive state or to what intent the transmission resource is requested.The eNB that has received the preamble identifies the sub-groupbelonging to the preamble, and allocates timing advance (TA) andtransmission resources to the UE so that the UE can match the timing ina random access response (RAR) so as to transmit the data in the RRCinactive mode (at step 2 s-15).

If the RAR message is received, the UE reestablishes PDCP devices andRLC devices for SRBs/DRBs, and if there exists nexthopchainingcount(NCC) received when the UE is shifted from the RRC connected mode to theRRC inactive mode, the UE may calculate new security keys (KeNB) usingthe NCC, and the PDCP device may perform ciphering and integrityprotection using the security keys. A MAC device and a PHY device areset based on the setup stored in the UE context. If the above-describedprocedure is completed, the UE generates an RRC connection resumerequest message (or MAC CE) to prepare transmission through the SRB (orDRB) and to prepare transmission through the DRB by processing the data.The MAC device multiplexes an RRC message to be transmitted through theSRB and data to be transmitted through the DRB to configure one MAC PDU,and transmits the MAC PDU in one TTI (at step 2 s-20). After message 3is transmitted as described above, HARQ ACK/NACK transmission may besupported. The message may include the BSR to indicate the amount ofdata remaining in the UE, and may include an indication indicating thatthe UE continuously remains in the RRC inactive mode. Further, the UEidentification (resume ID) for discriminating the UE and a short MAC-Ifor integrity protection may be included in the message.

The eNB that has successfully received the RRC message and the data asdescribed above may identify the UE identification (resume ID), performretrieving of the UE context from an anchor eNB or a source eNB (eNBhaving the UE context), complete PDCP/RLC/MAC/PHY devices and securitysetup based on the UE context, notify of successful reception throughtransmission of the RRC message newly defined in response to the UE dataand the message, or the existing RRC message (RRC connection suspend,RRC connection resume, RRC connection release, or RRC connectionreject), and notify of contention resolution for the message 3. Whenindicating that the UE is in the inactive mode, the eNB may include anindication for this in the RRC connection resume message to betransmitted, and if it is desired to shift the UE to an idle mode, theeNB may transmit the RRC connection resume message. Further, in case offirst suspending the transmission, the eNB may transmit an RRCconnection suspend message, and when re-connection after interruptingthe connection, the eNB may transmit the RRC connection reject message.When pre-engagement or setup, the eNB may transmit the message to theMAC CE (at step 2 s-25). The ACK of the data may be performed by the ARQof the RLC device.

If the UE in the RRC inactive mode transmits the data in the RRCinactive mode without shifting to the RRC connected mode, the batterypower consumption of the UE can be saved, and the signaling overhead ofthe network can be reduced.

FIG. 2T is a flowchart of a method of a terminal in an RRC inactive modenot shifted to an RRC connected mode, but transmits uplink data in theRRC inactive mode, according to an embodiment of the present disclosure.

If uplink data is generated, a UE at step 2 t-05 in an RRC inactive modemay perform a random access procedure to set a connection to a network.The UE reestablishes PDCP devices and RLC devices for SRBs/DRBs usingthe stored UE context, and if there exists NCC received when the UE isshifted from the RRC connected mode to the RRC inactive mode, the UE maycalculate new security keys (KeNB) using the NCC, and the PDCP devicemay perform ciphering and integrity protection using the security keys.A MAC device and a PHY device are set based on the setup stored in theUE context. After the above-described procedure, the UE may transmit apreamble, an RRC connection resume request message, and data at a timein the RRC inactive mode using a network and a pre-engaged contentionbased resource (at step 2 t-10). That is, the MAC device multiplexes anRRC connection resume request message to be transmitted through thepreamble and SRB0 and data to be transmitted through the DRB toconfigure one MAC PDU, and transmits the MAC PDU in one TTI at a time.If the number of resources to be transmitted by the UE is larger thanthe number of contention based resources, the MAC PDU may include theBSR in order to be allocated with an additional transmission resource,and may include the UE identification (resume ID) in order to identifythe UE.

The eNB may identify the UE identification (resume ID), performretrieving of the UE context from an anchor eNB or a source eNB (eNBhaving the UE context), complete PDCP/RLC/MAC/PHY devices and securitysetup based on the UE context, notify of successful reception throughtransmission of the RAR together with the RRC message newly defined inresponse to the UE data and the message, or the existing RRC message(RRC connection suspend, RRC connection resume, RRC connection release,or RRC connection reject), and notify of contention resolution at step 2t-15. When indicating that the UE is in the inactive mode, the eNB mayinclude an indication for this in the RRC connection resume message tobe transmitted, and if it is desired to shift the UE to an idle mode,the eNB may transmit the RRC connection resume message. When firstsuspending the transmission, the eNB may transmit an RRC connectionsuspend message, and when re-connection after interrupting theconnection, the eNB may transmit the RRC connection reject message. Whenpre-engagement or setup, the eNB may transmit the message to the MAC CE.The ACK of the data may be performed by the ARQ of the RLC device. TheMAC device of the eNB may multiplex the RAR, the RRC message, and theRLC ACK to configure one MAC PDU to be transmitted into one TTI.

If the UE in the RRC inactive mode transmits the data in the RRCinactive mode without shifting to the RRC connected mode, the batterypower consumption of the UE can be saved, and the signaling overhead ofthe network can be reduced.

FIG. 2U is a diagram of a terminal, according to an embodiment of thepresent disclosure.

The terminal includes an RF processor 2 u-10, a baseband processor 2u-20, a storage unit 2 u-30, and a controller 2 u-40.

The RF processor 2 u-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. That is, the RF processor 2 u-10 performs up-conversionof a baseband signal provided from the baseband processor 2 u-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 2 u-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, and an ADC. Although only one antenna is illustratedin the drawing, the terminal may be provided with a plurality ofantennas. The RF processor 2 u-10 may include a plurality of RF chains.The RF processor 2 u-10 may perform beamforming, and for thebeamforming, the RF processor 2 u-10 may adjust phases and sizes ofsignals transmitted or received through the plurality of antennas orantenna elements. The RF processor may perform MIMO, and may receiveseveral layers during performing of a MIMO operation. The RF processor 2u-10 may perform reception beam sweeping through proper configuration ofthe plurality of antennas or antenna elements under the control of thecontroller, or may control the direction and the beam width of thereception beam so that the reception beam is synchronized with thetransmission beam.

The baseband processor 2 u-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the system. During data transmission, the baseband processor 2 u-20generates complex symbols by encoding and modulating a transmitted bitstring. During data reception, the baseband processor 2 u-20 restores areceived bit string by demodulating and decoding the baseband signalprovided from the RF processor 2 u-10. For example, following an OFDMmethod, during data transmission, the baseband processor 2 u-20generates complex symbols by encoding and modulating a transmitted bitstring, performs mapping of the complex symbols on subcarriers, and thenconfigures OFDM symbols through the IFFT operation and CP insertion.During data reception, the baseband processor 2 u-20 divides thebaseband signal provided from the RF processor 2 u-10 in the unit ofOFDM symbols, restores the signals mapped on the subcarriers through theFFT operation, and then restores the received bit string throughdemodulation and decoding.

The baseband processor 2 u-20 and the RF processor 2 u-10 may be calleda transmitter, a receiver, a transceiver, or a communication unit. Inorder to support different radio connection technologies, at least oneof the baseband processor 2 u-20 and the RF processor 2 u-10 may includea plurality of communication modules. In order to process signals ofdifferent frequency bands, at least one of the baseband processor 2 u-20and the RF processor 2 u-10 may include different communication modules.The different radio connection technologies may include an LTE networkand an NR network. The different frequency bands may include super highfrequency (SHF) (e.g., 2.5 GHz or 5 GHz) band and millimeter wave(mmWave) (e.g., 60 GHz) band.

The storage unit 2 u-30 stores a basic program for an operation of theterminal, application programs, and data of setup information. Thestorage unit 2 u-30 provides stored data in accordance with a requestfrom the controller 2 u-40. The controller 2 u-40 controls the terminal.The controller 2 u-40 transmits and receives signals through thebaseband processor 2 u-20 and the RF processor 2 u-10. Further, thecontroller 2 u-40 records or reads data in or from the storage unit 2u-30. The controller 2 u-40 may include at least one processor, and mayinclude a communication processor for communication, and an AP forcontrolling an upper layer, such as an application program.

The controller 2 u-40 may be configured to receive from a base station apaging message for switching the terminal in an RRC inactive mode to anRRC idle mode, to transmit an RRC message to the base station based onreception of the paging message, to receive an RRC connection releasemessage from the base station, and to switch to the RRC idle mode basedon the RRC connection release message.

Further, the base station may store a context of the terminal, and ifthe paging message is triggered by the base station, the paging messagemay include an identification for identifying the terminal in the RRCinactive mode. The RRC message may be an RRC connection resume requestmessage.

If the paging message is transmitted from a core network node, thepaging message may include at least one of an S-TMSI and an IMSI. TheRRC message may be an RRC connection request message.

FIG. 2V is a diagram of a base station in a wireless communicationsystem, according to an embodiment of the present disclosure.

The base station includes an RF processor 2 v-10, a baseband processor 2v-20, a backhaul communication unit 2 v-30 (communication unit), astorage unit 2 v-40, and a controller 2 v-50.

The RF processor 2 v-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. The RF processor 2 v-10 performs up-conversion of abaseband signal provided from the baseband processor 2 v-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 2 v-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, and an ADC. Although only one antenna is illustrated,the first connection node may be provided with a plurality of antennas.The RF processor 2 v-10 may include a plurality of RF chains. The RFprocessor 2 v-10 may perform beamforming, and for the beamforming, theRF processor 2 v-10 may adjust phases and sizes of signals transmittedor received through the plurality of antennas or antenna elements. TheRF processor may perform down MIMO operation through transmission of oneor more layers.

The baseband processor 2 v-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the first radio connection technology. During data transmission, thebaseband processor 2 v-20 generates complex symbols by encoding andmodulating a transmitted bit string. During data reception, the basebandprocessor 2 v-20 restores a received bit string by demodulating anddecoding the baseband signal provided from the RF processor 2 v-10. Whenfollowing an OFDM method, during data transmission, the basebandprocessor 2 v-20 generates complex symbols by encoding and modulating atransmitted bit string, performs mapping of the complex symbols onsubcarriers, and then configures OFDM symbols through the IFFT operationand CP insertion. During data reception, the baseband processor 2 v-20divides the baseband signal provided from the RF processor 2 v-10 in theunit of OFDM symbols, restores the signals mapped on the subcarriersthrough the FFT operation, and then restores the received bit stringthrough demodulation and decoding. The baseband processor 2 v-20 and theRF processor 2 v-10 may be called a transmitter, a receiver, atransceiver, or a wireless communication unit.

The communication unit 2 v-30 provides an interface for performingcommunication with other nodes in the network.

The storage unit 2 v-40 stores a basic program for an operation of themain base station, application programs, and data of setup information.The storage unit 2 v-40 may store information on a bearer allocated tothe connected terminal and the measurement result reported from theconnected terminal. The storage unit 2 v-40 may store information thatbecomes a basis of determination whether to provide or suspend amulti-connection to the terminal. The storage unit 2 v-40 providesstored data in accordance with a request from the controller 2 v-50.

The controller 2 v-50 controls the main base station. The controller 2v-50 transmits and receives signals through the baseband processor 2v-20 and the RF processor 2 v-10 or through the communication unit 2v-30. Further, the controller 2 v-50 records or reads data in or fromthe storage unit 2 v-40. The controller 2 v-50 may include at least oneprocessor. The controller 2 v-50 may be configured to transmit to aterminal a paging message for switching the terminal in an RRC inactivemode to an RRC idle mode, to receive an RRC message from the terminal,and to transmit an RRC connection release message to the terminal basedon the RRC message. The RRC connection release message may indicateswitching of the terminal to the RRC idle mode.

The base station may store a context of the terminal, and if the pagingmessage is triggered by the base station, the paging message may includean identification for identifying the terminal in the RRC inactive mode.The RRC message may be an RRC connection resume request message.

If the paging message is transmitted from a core network node, thepaging message may include at least one of an S-TMSI and an IMSI. TheRRC message may be an RRC connection request message.

Embodiment 3

FIG. 3A is a diagram of an LTE system, according to an embodiment of thepresent disclosure.

A RAN of an LTE system includes ENBs 3 a-05, 3 a-10, 3 a-15, and 3 a-20,an MME 3 a-25, and an S-GW 3 a-30. A UE 3 a-35 accesses to an externalnetwork through the ENBs 3 a-05, 3 a-10, 3 a-15, and 3 a-20 and the S-GW3 a-30.

In FIG. 3A, the ENBs 3 a-05, 3 a-10, 3 a-15, and 3 a-20 correspond to anexisting node B of a UMTS system. The ENB 3 a-05 is connected to the UE3 a-35 on a radio channel, and plays a more complicated role than thatof the existing node B. In the LTE system, since all user trafficsincluding a real-time service, such as a VoIP through an internetprotocol, are serviced on shared channels, devices performing schedulingthrough consolidation of state information, such as a buffer state, anavailable transmission power state, and a channel state of each UE, arenecessary, and the ENBs 3 a-05, 3 a-10, 3 a-15, and 3 a-20 correspond tosuch scheduling devices. One ENB controls a plurality of cells. In orderto implement a transmission speed of 100 Mbps, the LTE system uses OFDMin a bandwidth of 20 MHz as an RAT. The LTE system adopts an AMC schemethat determines a modulation scheme and a channel coding rate to matchthe channel state of the terminal. The S-GW 3 a-30 is a device thatprovides a data bearer, and generates or removes the data bearer underthe control of the MME 3 a-25. The MME 3 a-25 is a device that takescharge of not only mobility management of the UE 3 a-35 but also variouskinds of control functions, and is connected to the plurality of ENBs 3a-05, 3 a-10, 3 a-15, and 3 a-20.

FIG. 3B is a diagram of a radio protocol structure in an existing LTEsystem, according to an embodiment of the present disclosure.

In a UE or an ENB, a radio protocol of an LTE system includes a PDCP 3b-05 or 3 b-40, an RLC 3 b-10 or 3 b-35, and a MAC 3 b-15 or 3 b-30. ThePDCP 3 b-05 or 3 b-40 takes charge of IP headercompression/decompression operations. The main functions of the PDCP aresummarized as follows:

-   -   Header compression and decompression: ROHC only.    -   Transfer of user data;    -   In-sequence delivery of upper layer PDUs at a PDCP        reestablishment procedure for an RLC AM;    -   For split bearers in DC (only support for an RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception;    -   Duplicate detection of lower layer SDUs at a PDCP        reestablishment procedure for an RLC AM;    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at a PDCP data-recovery procedure, for an        RLC AM;    -   Ciphering and deciphering; and    -   Timer-based SDU discard in an uplink.

The RLC 3 b-10 or 3 b-35 reconfigures a PDCP PDU with a proper size andperforms an ARQ operation and the like. The main functions of the RLCare summarized as follows.

-   -   Transfer of upper layer PDUs;    -   Error correction through an ARQ (only for AM data transfer);    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer);    -   Re-segmentation of RLC data PDUs (only for UM and AM data        transfer);    -   Reordering of RLC data PDUs (only for UM and AM data transfer);    -   Duplicate detection (only for UM and AM data transfer);    -   Protocol error detection (only for AM data transfer);    -   RLC SDU discard (only for UM and AM transfer); and    -   RLC reestablishment.

The MAC 3 b-15 or 3 b-30 is connected to several RLC layer devicesconfigured in one terminal, and performs multiplexing/demultiplexing ofRLC PDUs into/from MAC PDU. The main functions of the MAC are summarizedas follows:

-   -   Mapping between logical channels and transport channels;    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from TB transferred to/from the        physical layer on transport channels;    -   Scheduling information reporting;    -   Error correction through HARQ;    -   Priority handling between logical channels of one UE;    -   Priority handling between UEs by means of dynamic scheduling;    -   MBMS service identification;    -   Transport format selection; and    -   padding.

The physical layer 3 b-20 or 3 b-25 performs channel coding andmodulation of upper layer data to configure and transmit OFDM symbols ona radio channel, or performs demodulation and channel decoding of theOFDM symbols received on the radio channel to transfer the demodulatedand channel-decoded symbols to an upper layer.

FIG. 3C is a diagram of a DRX operation, according to an embodiment ofthe present disclosure. The DRX is applied to minimize power consumptionof the UE, and is a monitoring technology only in a predetermined PDCCHin order to obtain scheduling information. The DRX can be performed inboth a standby mode and a connected mode, and the operating methods aresomewhat different from each other. As described herein, in theconnected mode, if the UE continuously monitors a PDCCH to acquire thescheduling information, it may cause great power consumption. The basicDRX operation has a DRX period at 3 c-00, and the PDCCH is monitoredonly for an on-duration time at 3 c-05. In the connected mode, the DRXperiod is configured to have a long DRX and a short DRX. The long DRXperiod is applied, and if needed, the eNB may trigger the short DRXperiod using a MAC CE. After a predetermined time elapses, the UE ischanged from the short DRX period to the long DRX period. Initialscheduling information of a specific UE is provided only on the PDCCH.Accordingly, the UE periodically monitors only the PDCCH, and, thus,power consumption can be minimized.

If scheduling information on a new packet is received on the PDCCH forthe on-duration time at 3 c-05 (3 c-10), the UE starts a DRX inactivitytimer at 3 c-15. The UE maintains in an active state for the DRXinactivity timer. That is, the UE continues the PDCCH monitoring. The UEalso starts an HARQ RTT timer at 3 c-20. The HARQ RTT timer is appliedto prevent the UE from unnecessarily monitoring the PDCCH for the HARQRTT, and during the timer operating time, the UE is not required toperform the PDCCH monitoring. However, while the PRX inactivity timerand the HARQ RTT timer operate simultaneously, the UE continues thePDCCH monitoring based on the DRX inactivity timer. If the HARQ RTTtimer expires, a DRX retransmission timer at 3 c-25 starts. While theDRX retransmission timer operates, the UE should perform the PDCCHmonitoring. During the DRX retransmission timer operating time, thescheduling information for the HARQ retransmission is received (at 3c-30). If the scheduling information is received, the UE immediatelysuspends the DRX retransmission timer, and starts the HARQ RTT timeragain. The above-described operation continues until the packet issuccessfully received (at 3 c-35).

Setup information related to the DRX operation in the connected mode istransferred to the UE through the RRCConnectionReconfiguration message.The on-duration timer, the DRX inactivity timer, and the DRXretransmission timer are defined by the number of PDCCH subframes. If apredetermined number of subframes that are defined as PDCCH subframeshave passed after the timer starts, the timer expires. In FDD, alldownlink subframes belong to PDCCH subframes, and in TDD, downlinksubframes and special subframes correspond to them. In the TDD, downlinksubframes, uplink subframes, and special subframes exist in the samefrequency band. Among them, the downlink subframes and the specialsubframes are considered as the PDCCH subframes.

The eNB may configure two kinds of states longDRX and shortDRX. The eNBmay use one of two states in consideration of power preferenceindication information and UE mobility record information typicallyreported from the UE, and the characteristic of the configured DRB.Shifting between the two states is performed by transmitting whether aspecific timer has expired or a specific MAC CE to the UE.

In the existing LTE technology, only two kinds of DRX periods can beconfigured, and thus it is not possible to dynamically change the DRXperiod in accordance with various DRB characteristics, traffic patterns,and buffer states.

A DRX operation capable of dynamically changing the DRX period ordrx-Inactivity Timer in accordance with various DRB characteristics,traffic patterns, and buffer states is described herein. The DRXoperation is featured to configure a default DRX period or defaultdrx-InactivityTimer and to dynamically change the DRX period using theMAC CE. Also described herein is a scheme for the UE to maintain anactive time through suspending of the configured DRX operation if the UEreports beam measurement, and in particular, new optimum beams.

FIG. 3D is a diagram of a delay phenomenon due to a DRX while a handoveris triggered in an LTE system, according to an embodiment of the presentdisclosure.

If an eNB configures a DRX operation to a UE in a connected mode, the UEmonitors a PDCCH for an on-duration time period at 3 d-05 for eachconfigured DRX period. When applying an eDRX, the DRX period at 3 d-20can be configured up to 10.24 sec at maximum. Further, the eNB canconfigure cell measurement to the UE. The cell measurement is to supportmobility of the UE. If a specific event occurs, the UE reports collectedcell measurement information to the eNB (at 3 d-10). Based on the LTEsystem, report events are as follows. Even the next-generation mobilecommunication system may have events corresponding to events applied tothe LTE as below:

Event A1: Serving becomes better than absolute threshold:

Event A2: Serving becomes worse than absolute threshold;

Event A3: Neighbor becomes amount of offset better than a primaryserving cell (PCell)/secondary serving cell (SCell);

Event A4: Neighbor becomes better than absolute threshold;

Event A5: PCell/SCell becomes worse than absolute threshold1 ANDNeighbor becomes better than another absolute threshold2.

Event A6: Neighbor becomes amount of offset better than SCell.

Event C1: channel state information reference signal (CSI-RS) resourcebecomes better than absolute threshold;

Event C2: CSI-RS resource becomes amount of offset better than referenceCSI-RS resource.

Event B1: Neighbor becomes better than absolute threshold;

Event B2: PCell becomes worse than absolute threshold1 and Neighborbecomes better than another absolute threshold2.

Event W1: wireless local area network (WLAN) becomes better than athreshold;

Event W2: All WLAN inside WLAN mobility set become worse than athreshold1 and a WLAN outside WLAN mobility set becomes better than athreshold2: and

Event W3: All WLAN inside WLAN mobility set become worse than athreshold.

Among the above events, event A3 may be data for the eNB to determinehandover trigger. If the condition of the event A3 is satisfied and theUE reports cell measurement information (at 3 d-10), the eNB triggers ahandover based on the cell measurement report (at 3 d-15). Although onlythe event A3 is mentioned, the eNB can use other report events indetermining the handover. If the eNB determines the handover, it shouldconfigure this to the UE. Since the UE is performing the DRX, the eNB isunable to directly transfer this to the UE, and thus it waits until thenext on-duration arrives (at 3 d-25). If the on-duration arrives, theeNB transmits a message including a PDCCH including schedulinginformation and the handover setup information (at 3 d-30). In the LTE,the message is an RRCConnectionReconfiguration. The UE that has receivedthe message performs a handover operation (at 3 d-35). In the DRXoperation, since downlink scheduling has been performed during theon-duration, a drx-inactivity timer is operated (at 3 d-40). Through theabove-described process, the eNB may determine the handover, and mayidentify delay phenomenon occurrence due to the DRX driving until theeNB configures this to the UE (at 3 d-25). In consideration of the UEmoving rapidly to a neighboring cell, this may cause a handover failure.Further, in consideration of a long period of the eDRX, such failureprobability may be increased.

FIG. 3E is a flowchart of a method for temporarily suspending a DRXwhile triggering a handover, according to an embodiment of the presentdisclosure.

A scheme for a UE to temporarily suspend a DRX driven by the UE if it isdetermined that it is influential to perform a handover in order toprevent a handover delay phenomenon due to the existing DRX operation.In particular, when performing temporal DRX suspend in accordance with aspecific condition, the UE is featured to report this to an eNB througha new MAC CE. The basis on which the eNB determines whether to performthe handover with the cell measurement information reported by the UE inan actual network corresponds to network implementation, and it is notpossible to accurately determine this only in consideration of the cellmeasurement information reported by the UE. The DRX driving statebetween the network and the UE may be wrongly understood. Accordingly,when performing the DRX suspend based on the cell measurementinformation reported by the UE, the DRX driving state may be preventedfrom being wrongly understood through accurate indication to the networkusing the MAC CE. If the triggered DRX suspend is not necessary, thenetwork indicates to restart the DRX.

If the eNB configures the DRX operation to the UE in the connected mode,the UE monitors a PDCCH for an on-duration time period at step 3 e-05for each configured DRX period. Further, the eNB may configure the cellmeasurement to the UE. The UE reports the collected cell measurementinformation to the eNB periodically or when a specific event occurs (atstep 3 e-10). Since a report event has already been described based onan LTE system, even the next-generation mobile communication system mayhave an event corresponding to the event applied to the LTE. Among them,event A3 may be data for the eNB to determine the handover trigger. Ifthe condition of the event A3 is satisfied and the UE reports the cellmeasurement information (at step 3 e-10), the eNB triggers the handoverbased on the cell measurement report (at step 3 e-20).

If it is determined that the cell measurement information can cause theeNB to trigger the handover when the UE reports the cell measurementinformation, the UE may include a new MAC CE together with the cellmeasurement information (at step 3 e-10). The new MAC CE is used tonotify that the UE temporarily suspends the DRX. Since the new MAC CE isfor the purpose of notifying of the temporal DRX suspend, it is composedof only a subheader, and is featured not to have a payload portioncorresponding to the subheader. Further, the contents of the DRX suspendoperation may be included in the payload portion. For example, timeinformation for the UE to temporarily suspend the DRX may be includedtherein. Although only the event A3 is mentioned as the determinationbasis for triggering the handover, the eNB may use other report eventsin determining the handover. The UE that has transmitted the messageincluding the MAC CE to the eNB temporarily suspends the DRX beingdriven just after the message transmission or after a predetermined timeelapses (at steps 3 e-15 and 3 e-30). The reason why the predeterminedtime is considered is that it is not possible to receive actual handoversetup information just after the report transmission. Accordingly, thestart of the DRX suspend may be adjusted on the dimension of saving thepower consumption of the UE. If the eNB determines the handover (at step3 e-20), it should configure this to the UE. Since the UE hastemporarily suspended the DRX, it can directly transfer theconfiguration to the UE (at step 3 e-35), and, thus, it is not necessaryto wait until the next on-duration arrives. The eNB transmits a controlplane control message including the PDCCH including the schedulinginformation and the handover setup information simultaneously withdetermining the handover trigger (at step 3 e-35). The UE that hasreceived the message performs the handover operation (at step 3 e-40).The handover delay time at step 3 e-25 can be shortened. If thepredetermined condition is satisfied, the DRX operation may restart (atstep 3 e-45).

FIG. 3F is a flowchart of a method between a UE and an eNB, according toan embodiment of the present disclosure.

The UE 3 f-05 and the eNB 3 f-10 identify whether they support DRXsuspend functions with each other (at step 3 f-15). The UE 3 f-05reports performance capabilities for its own DRX suspend functions tothe eNB 3 f-10 using a specific RRC message. Through system informationbeing broadcasted, the eNB 3 f-10 indicates that it can support the DRXsuspend functions to UEs existing in its service area. The eNB 3 f-10transmits setup information related to cell measurement and DRX and DRXsuspend setup information to the UE 3 f-05 through the RRC message (atstep 3 f-20). The DRX suspend setup information include time information(timer value, e.g., a DRX suspend timer) in which the UE 3 f-05temporarily suspends the DRX driving. The UE 3 f-05 that has receivedthis immediately applies the setup information, and performs relatedcell measurement and DRX operation (at step 3 f-25). The DRX operationmay start after a specific MAC CE is received (at step 3 f-30).

The UE 3 f-05 periodically measures serving and neighboring cellsreceived from the eNB 3 f-10, and a report event indicating necessity ofthe handover is triggered (at step 3 f-35). The UE 3 f-05 reports thisto the eNB 3 f-10, and in this case, it includes the MAC CE indicatingtemporal suspend of the DRX being driven in accordance with the handoverperformance possibility in the report (at step 3 f-40). The UE 3 f-05drives the configured DRX suspend timer (at step 3 f-45). The UE 3 f-05temporarily suspends the DRX driving until the timer expires. If anothercondition is satisfied in addition to the timer expiration, the UE 3f-05 may resume the DRX driving. The UE may restart the DRX driving ifthe following conditions are satisfied:

-   -   When the DRX suspend timer configured by the eNB expires;    -   When a control plane control message indicating the handover is        received from the eNB; and    -   When its scheduling information (DL assignment or UL grant) is        received.

The UE 3 f-05 receives the control plane control message indicating thehandover from the eNB 3 f-10 (at step 3 f-50). The UE 3 f-05 releasesthe DRX suspend (at step 3 f-55). The UE 3 f-05 re-drives the DRXoperation that has temporarily been suspended (at step 3 f-60).

FIG. 3G is a flowchart of a method of a terminal, according to anembodiment of the present disclosure.

At step 3 g-05, the UE receives setup information on the cellmeasurement and DRX and DRX suspend operations from the eNB. At step 3g-10, the UE starts the cell measurement and DRX operation just afterreceiving the setup information or at a specific time. At step 3 g-15,the UE periodically performs cell measurement, and triggers a cellmeasurement report if a report event causing the handover occurs. Atstep 3 g-20, the UE reports the collected cell measurement informationto the eNB, and during the reporting, the UE includes the MAC CEnotifying of the temporal suspend of the DRX being driven in the report.At step 3 g-25, the UE temporarily suspends the DRX operation beingdriven, and maintains active time. At step 3 g-30, the active time ismaintained for a specific time or until a specific event occurs, andthereafter, the UE re-drives the DRX operation immediately or at aspecific time.

FIG. 3H is a flowchart of a method of a base station, according to anembodiment of the present disclosure.

At step 3 h-05, the eNB transmits setup information on the cellmeasurement and DRX and DRX suspend operations. At step 3 h-10, the eNBreceives a report of cell measurement information from the UE. At step 3h-15, the eNB triggers a handover based on the cell measurementinformation. At step 3 h-20, the eNB determines whether the MAC CEnotifying that the UE temporarily suspends the DRX being driven isincluded in the report. If the MAC CE is included, the eNB, at step 3h-25, transmits handover setup information to the UE without delay.Otherwise, at step 3 h-30, the eNB transmits the handover setupinformation after waiting up to the arriving on-duration.

FIG. 3I is a diagram of a MAC CE indicating a temporal DRX suspend,according to an embodiment of the present disclosure.

A new MAC CE for notifying of temporary suspend of the DRX driven by theUE is now herein described. The MAC CE is composed of only a subheader,and the subheader of the new MAC CE includes a specific logical channelidentifier (LCID) at 3 i-05 indicating this. Since the MAC CE does nothave a payload portion, there is not an L field indicating the size ofthe payload portion in the subheader.

As an alternative, the MAC CE having the payload may be considered. Inthe payload portion, time information at 3 i-10 for the UE totemporarily suspend the DRX being driven may be included. Theinformation may coincide or may not coincide with the DRX suspend timerconfigured by the eNB.

FIG. 3J is a diagram of a terminal, according to an embodiment of thepresent disclosure.

The terminal includes an RF processor 3 j-10, a baseband processor 3j-20, a storage unit 3 j-30, and a controller 3 j-40.

The RF processor 3 j-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. The RF processor 3 j-10 performs up-conversion of abaseband signal provided from the baseband processor 3 j-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 3 j-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, and an ADC. Although only one antenna is illustratedin FIG. 3J, the terminal may be provided with a plurality of antennas.The RF processor 3 j-10 may include a plurality of RF chains. The RFprocessor 3 j-10 may perform beamforming, and for the beamforming, theRF processor 3 j-10 may adjust phases and sizes of signals transmittedor received through the plurality of antennas or antenna elements. TheRF processor may perform MIMO, and may receive several layers duringperforming of a MIMO operation.

The baseband processor 3 j-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the system. During data transmission, the baseband processor 3 j-20generates complex symbols by encoding and modulating a transmitted bitstring. During data reception, the baseband processor 3 j-20 restores areceived bit string by demodulating and decoding the baseband signalprovided from the RF processor 3 j-10. When following an OFDM method,during data transmission, the baseband processor 3 j-20 generatescomplex symbols by encoding and modulating a transmitted bit string,performs mapping of the complex symbols on subcarriers, and thenconfigures OFDM symbols through the IFFT operation and CP insertion.Further, during data reception, the baseband processor 3 j-20 dividesthe baseband signal provided from the RF processor 3 j-10 in the unit ofOFDM symbols, restores the signals mapped on the subcarriers through theFFT operation, and then restores the received bit string throughdemodulation and decoding.

The baseband processor 3 j-20 and the RF processor 3 j-10 may be calleda transmitter, a receiver, a transceiver, or a communication unit. Inorder to support different radio connection technologies, at least oneof the baseband processor 3 j-20 and the RF processor 3 j-10 may includea plurality of communication modules. Further, in order to processsignals of different frequency bands, at least one of the basebandprocessor 3 j-20 and the RF processor 3 j-10 may include differentcommunication modules. For example, the different radio connectiontechnologies may include a radio local area network (LAN) (e.g., IEEE802.11) and a cellular network (e.g., LTE). Further, the differentfrequency bands may include SHF (e.g., 2.5 GHz or 5 GHz) band andmillimeter wave (mmWave) (e.g., 60 GHz) band.

The storage unit 3 j-30 stores a basic program for an operation of theterminal, application programs, and data of setup information. Thestorage unit 3 j-30 may store therein information related to a secondaccess node performing wireless communication using a second radioconnection technology. The storage unit 3 j-30 provides stored data inaccordance with a request from the controller 3 j-40.

The controller 3 j-40 controls the terminal. The controller 3 j-40transmits and receives signals through the baseband processor 3 j-20 andthe RF processor 3 j-10. The controller 3 j-40 records or reads data inor from the storage unit 3 j-30. The controller 3 j-40 may include atleast one processor, and may include a communication processor forcommunication and an AP for controlling an upper layer, such as anapplication program.

FIG. 3K is a diagram of a base station in a wireless communicationsystem, according to an embodiment of the present disclosure.

The base station includes an RF processor 3 k-10, a baseband processor 3k-20, a backhaul communication unit (communication unit) 3 k-30, astorage unit 3 k-40, and a controller 3 k-50.

The RF processor 3 k-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. The RF processor 3 k-10 performs up-conversion of abaseband signal provided from the baseband processor 3 k-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 3 k-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, and an ADC. Although only one antenna is illustrated,the first connection node may be provided with a plurality of antennas.The RF processor 3 k-10 may include a plurality of RF chains. The RFprocessor 3 k-10 may perform beamforming, and for the beamforming, theRF processor 3 k-10 may adjust phases and sizes of signals transmittedor received through the plurality of antennas or antenna elements. TheRF processor may perform down MIMO operation through transmission of oneor more layers.

The baseband processor 3 k-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the first radio connection technology. During data transmission, thebaseband processor 3 k-20 generates complex symbols by encoding andmodulating a transmitted bit string. During data reception, the basebandprocessor 3 k-20 restores a received bit string by demodulating anddecoding the baseband signal provided from the RF processor 3 k-10. Whenfollowing an OFDM method, during data transmission, the basebandprocessor 3 k-20 generates complex symbols by encoding and modulating atransmitted bit string, performs mapping of the complex symbols onsubcarriers, and then configures OFDM symbols through the IFFT operationand CP insertion. During data reception, the baseband processor 3 k-20divides the baseband signal provided from the RF processor 3 k-10 in theunit of OFDM symbols, restores the signals mapped on the subcarriersthrough the FFT operation, and then restores the received bit stringthrough demodulation and decoding. The baseband processor 3 k-20 and theRF processor 3 k-10 may be called a transmitter, a receiver, atransceiver, or a wireless communication unit.

The communication unit 3 k-30 provides an interface for performingcommunication with other nodes in the network. The backhaulcommunication unit 3 k-30 converts a bit string transmitted from themain eNB to another node, for example, an auxiliary eNB or a corenetwork into a physical signal, and converts the physical signalreceived from the other node into the bit string.

The storage unit 3 k-40 stores a basic program for an operation of themain base station, application programs, and data of setup information.The storage unit 3 k-40 may store information on a bearer allocated tothe connected terminal and the measurement result reported from theconnected terminal. The storage unit 3 k-40 may store information thatbecomes a basis of determination whether to provide or suspend amulti-connection to the terminal. The storage unit 3 k-40 providesstored data in accordance with a request from the controller 3 k-50.

The controller 3 k-50 controls the main base station. The controller 3k-50 transmits and receives signals through the baseband processor 3k-20 and the RF processor 3 k-10 or through the communication unit 3k-30. The controller 3 k-50 records or reads data in or from the storageunit 3 k-40. The controller 3 k-50 may include at least one processor.

Embodiment 4

FIG. 4A is a diagram of an LTE system, according to an embodiment of thepresent disclosure.

A wireless communication system includes ENBs 4 a-05, 4 a-10, 4 a-15,and 4 a-20, an MME 4 a-25, and an S-GW 4 a-30. A UE 4 a-35 accesses toan external network through the ENBs 4 a-05, 4 a-10, 4 a-15, and 4 a-20and the S-GW 4 a-30.

The ENBs 4 a-05, 4 a-10, 4 a-15, and 4 a-20 are access nodes of acellular network, and provide radio accesses to the UEs accessing thenetwork. The ENBs 4 a-05, 4 a-10, 4 a-15, and 4 a-20 support connectionsbetween the UEs and a CN by performing scheduling through consolidationof state information, such as a buffer state, an available transmissionpower state, and a channel state of each UE, in order to service users'traffics. The MME 4 a-25 takes charge of not only mobility management ofthe UE 4 a-35 but also various kinds of control functions, and isconnected to the plurality of eNBs 4 a-05, 4 a-10, 4 a-15, and 4 a-20.The S-GW 4 a-30 provides a data bearer. Further, the MME 4 a-25 and theS-GW 4 a-30 may further perform authentication of the UE 4 a-35 andbearer management, and process packets arriving from the eNBs 4 a-05, 4a-10, 4 a-15, and 4 a-20, or process packets to be transferred to theeNBs 4 a-05, 4 a-10, 4 a-15, and 4 a-20.

FIG. 4B is a diagram of a radio protocol structure in an LTE system,according to an embodiment of the present disclosure.

In a UE or an ENB, a radio protocol of an LTE system includes a PDCP 4b-05 or 4 b-40, an RLC 4 b-10 or 4 b-35, and a MAC 4 b-15 or 4 b-30. ThePDCP 4 b-05 or 4 b-40 takes charge of IP headercompression/decompression operations. The main functions of the PDCP aresummarized as follows:

-   -   Header compression and decompression: ROHC only;    -   Transfer of user data;    -   In-sequence delivery of upper layer PDUs at a PDCP        reestablishment procedure for an RLC AM;    -   For split bearers in DC (only support for an RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception;    -   Duplicate detection of lower layer SDUs at a PDCP        reestablishment procedure for an RLC AM;    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at a PDCP data-recovery procedure, for an        RLC AM;    -   Ciphering and deciphering; and    -   Timer-based SDU discard in an uplink.

The RLC 4 b-10 or 4 b-35 reconfigures a PDCP PDU with a proper size andperforms an ARQ operation and the like. The main functions of the RLCare summarized as follows:

-   -   Transfer of upper layer PDUs;    -   Error correction through an ARQ (only for AM data transfer);    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer);    -   Re-segmentation of RLC data PDUs (only for UM and AM data        transfer);    -   Reordering of RLC data PDUs (only for UM and AM data transfer);    -   Duplicate detection (only for UM and AM data transfer);    -   Protocol error detection (only for AM data transfer);    -   RLC SDU discard (only for UM and AM transfer); and    -   RLC reestablishment.

The MAC 4 b-15 or 4 b-30 is connected to several RLC layer devicesconfigured in one terminal, and performs multiplexing/demultiplexing ofRLC PDUs into/from MAC PDU. The main functions of the MAC are summarizedas follows:

-   -   Mapping between logical channels and transport channels;    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        transferred to/from the physical layer on transport channels;    -   Scheduling information reporting;    -   HARQ function (error correction through HARQ);    -   Priority handling between logical channels of one UE;    -   Priority handling between UEs by means of dynamic scheduling;    -   MBMS service identification;    -   Transport format selection; and    -   padding.

The physical layer 4 b-20 or 4 b-25 performs channel coding andmodulation of upper layer data to configure and transmit OFDM symbols ona radio channel, or performs demodulation and channel decoding of theOFDM symbols received on the radio channel to transfer the demodulatedand channel-decoded symbols to an upper layer.

Although not illustrated, RRC layers exist on upper portions of PDCPlayers of the UE and the eNB, and the RRC layers may transmit/receivesetup control messages related to accesses and measurement for radioresource control.

FIG. 4C is a diagram of carrier aggregation (CA) of an LTE system,according to an embodiment of the present disclosure.

Referring to FIG. 4C, one eNB 4 c-05 transmits and receivesmulti-carriers over several frequency bands. If a carrier 4 c-15 havinga forward center frequency of f1 and a carrier 4 c-15 having a forwardcenter frequency of f2 are transmitted from the eNB 4 c-05, in therelated art, one eNB transmits/receives data using one of the twocarriers. However, the UE having a carrier aggregation capability cansimultaneously transmit/receive data through several carriers. The eNB 4c-05 allocates more carriers to a UE 4 c-20 having the carrieraggregation capability, and, thus, the transmission speed of the UE 4c-20 can be heightened.

As described above, aggregation of forward carriers and backwardcarriers transmitted and received by one eNB is referred to as intra-eNBCA. Traditionally, if it is assumed that one forward carrier transmittedby one eNB and one backward carrier received by the one eNB constituteone cell, it may be understood that the CA is for the UE totransmit/receive data simultaneously through several cells. Throughthis, the maximum transmission speed is increased in proportion to thenumber of carriers being aggregated.

Hereinafter, reception of data by the UE through a certain forwardcarrier or transmission of data by the UE through a certain backwardcarrier has the same meaning as transmission/reception of data using acontrol channel and a data channel provided from a cell corresponding tothe center frequency and the frequency band featuring the carrier. TheCA will be particularly expressed as setup of a plurality of servingcells, and with respect to the serving cell, the PCell, SCell, oractivated serving cell will be used. The PCell and SCell are termsrepresenting the kind of serving cell set in the UE. There are somedifferent points between PCell and SCell, and for example, PCell alwaysmaintains an active state, but SCell repeats an active state andinactive state in accordance with the indication of the eNB. Theterminal mobility is controlled around PCell, and it may be understoodthat SCell is an additional serving cell for datatransmission/reception. PCell and SCell are defined in the LTE standards36.331 or 36.321. The terms have the same meanings as those used in anLTE mobile communication system. The terms carrier, component carrier,and serving cell are used interchangeably.

According to a normal intra-eNB CA, the UE transmits not only HARQfeedback for PCell and channel state information (CSI) but also HARQfeedback for SCell and CSI through a physical uplink control channel(hereinafter, PUCCH) of PCell. This is to apply the CA operation evenwith respect to the UE of which uplink simultaneous transmission is notpossible. In LTE release-13 (Rel-13) enhanced CA (eCA), an additionalSCell having a PUCCH is defined, and up to 32 carriers can beaggregated. The PUCCH SCell is limited to a serving cell belonging to amast cell group (MCG). The MCG includes a set of serving cellscontrolled by a master eNB (MeNB) controlling PCell, and the SCGincludes a set of serving cells controlled by an eNB that is not an eNBcontrolling PCell, in other words, a secondary eNB (SeNB), controllingonly SCells. The eNB notifies the UE whether a specific serving cellbelongs to the MCG or SCG in the process of setting the correspondingserving cell. The eNB notifies the UE whether the respective SCellbelong to the PCell group or the PUCCH SCell group.

FIG. 4D is a diagram of a next-generation mobile communication system,according to an embodiment of the present disclosure.

An RAN of a next-generation mobile communication system includes an NRENB 4 d-10 and an NR CN 4 d-05. An NR UE 4 d-15 accesses to an externalnetwork through the NR gNB 4 d-10 and the NR CN 4 d-05.

The NR gNB 4 d-10 corresponds to an ENB of the existing LTE system. TheNR gNB 4 d-10 is connected to the NR UE 4 d-15 on a radio channel, and,thus, it can provide a more superior service than the service of theexisting node B. Since all user traffics are serviced on shared channelsin the next-generation mobile communication system, a device thatperforms scheduling through consolidation of status information, such asa buffer state of NR UEs 4 d-15, an available transmission power state,and a channel state, is required, and the NR NB 4 d-10 takes charge ofthis. One NR gNB 4 d-10 generally controls a plurality of cells, and iscomposed of a central unit (CU) generalizing control and signaling and adistributed unit (DU) taking charge of signal transmission/reception. Inorder to implement ultrahigh-speed data transmission as compared withthe existing LTE, the NR may have a bandwidth that is equal to or higherthan the existing maximum bandwidth, and a beamforming technology may beadditionally grafted in consideration of OFDM as an RAT. Further, an AMCscheme determining a modulation scheme and a channel coding rate tomatch the channel state of the NR UE 4 d-15 is adopted. The NR CN 4 d-05performs functions of mobility support, bearer setup, and QoSconfiguration. The NR CN 4 d-05 is a device that takes charge of notonly a mobility management function of the NR UE 4 d-15 but also variouskinds of control functions, and is connected to a plurality of ENBs. Thenext-generation mobile communication system may interlock with theexisting LTE system, and the NR CN 4 d-05 is connected to an MME 4 d-25through a network interface. The MME 4 d-25 is connected to an ENB 4d-30 that is the existing ENB.

FIG. 4E is a flowchart of a method of a handover procedure of an LTEsystem, according to an embodiment of the present disclosure.

A UE 4 e-01 in a connected mode state reports cell measurementinformation to a current serving eNB 4 e-02 periodically or when aspecific event is satisfied (at step 4 e-05). The serving eNB/servingcell 4 e-02 determines whether the UE 4 e-01 proceeds with a handover toan adjacent cell based on the measurement information. The handover is atechnology to change the serving cell providing a service to the UE in aconnected mode state to another eNB. If the serving cell determines thehandover, it requests the handover by transmitting a handover (HO)request message to a new or target eNB 4 e-03 that will provide aservice to the UE 4 e-01, that is, the target eNB/target cell 4 e-03 (atstep 4 e-10). If the target 4 e-03 accepts the handover request, ittransmits an HO request ACK message to the eNB 4 e-02 (at step 4 e-15).The eNB 4 e-02 that has received the message transmits an HO commandmessage to the UE 4 e-01 (at step 4 e-20).

Before receiving the HO command, the UE 4 e-01 continuously receives adownlink channel physical downlink control channel/physical downlinkshared channel/physical hybrid-ARQ indicator channel (PDCCH/PDSCH/PHICH)from the eNB 4 e-02, and transmits an uplink channel physical uplinkshared channel/physical uplink control channel (PUSCH/PUCCH). The eNB 4e-02 (serving cell) transfers the HO command message to the UE using theRRC connection reconfiguration message (at step 4 e-20). If the messageis received, the UE 4 e-01 suspends data transmission/reception with theeNB 4 e-02, and starts a T304 timer. The T304 timer causes the UE 4 e-01to retrieve to the original setup and to be shifted to the RRC idlestate if the UE 4 e-01 has not succeeded in handover with respect to thetarget eNB 4 e-03 (target cell) for a specific time.

The eNB 4 e-02 transfers an SN status for uplink/downlink data, and ifthere is the downlink data, it transfers the downlink data to the targeteNB 4 e-03 (at steps 4 e-30 and 4 e-35). The UE 4 e-01 attempts a randomaccess to the target eNB 4 e-03 indicated from the eNB 4 e-02 (at step 4e-40). The random access is to notify the target eNB 4 e-03 that the UE4 e-01 moves through the handover and to match uplink synchronization.For the random access, the UE 4 e-01 transmits to the target eNB 4 e-03preambles corresponding to a preamble ID provided from the eNB 4 e-02and a preamble ID randomly selected. If a specific number of preambleshave passed after the preamble transmission, the UE 4 e-01 monitorswhether an RAR is transmitted from the target eNB 4 e-03. The monitoringtime period is called an RAR window.

If the RAR is received for the specific time period (at step 4 e-45),the UE 4 e-01 carries the handover complete message on anRRCConnectionReconfigurationComplete message to be transmitted to thetarget eNB 4 e-03 (at step 4 e-55). Thereafter, the UE 4 e-01 transmitsuplink channel PUSCH/PUCCH while continuously receiving downlink channelPDCCH/PDSCH/PHICH from the target eNB 4 e-03. If an RAR is successfullyreceived from the target eNB 4 e-03, the UE 4 e-01 ends the T304 timer(at step 4 e-50). The target eNB 4 e-03 requests a path switch tocorrect paths of bearers set to the serving eNB 4 e-01 (at steps 4 e-60and 4 e-65), and reports deletion of the UE context of the UE 4 e-01 tothe serving eNB 4 e-02 (at step 4 e-70). Accordingly, the UE 4 e-01attempts to receive data from the RAR window start time with respect tothe target eNB 4 e-03, and after receiving the RAR, the UE startstransmission of an RRCConnectionReconfigurationComplete message to thetarget eNB 4 e-03.

During the handover in the existing LTE, time interruption occurs whilethe random access procedure to the target eNB 4 e-03, and zero mobilityinterruption time for removing the time interruption is a requirement inthe NR. The handover in the existing LTE is classified into type 1handover, and the present disclosure compares the type 1 handover with aproposed method (e.g., type 2 handover).

A target PCell to which the handover is to be performed is a servingcell set to the UE, and if the handover between the serving cells isperformed, this is defined as type 2 handover. The type 2 handover maybe defined as the change of PCell between serving cells. For the type 2handover, the following conditions should be satisfied.

-   -   PUCCH connection setup of at least one serving cell excluding        PCell should be performed: this is because an uplink control        channel for HARQ feedback, scheduling request, and CSI        transmission is necessary.

In general, the type 2 handover is composed of the following 4 stages.

-   -   1. Phase 0: Stage in which a UE is connected to PCell.    -   2. Phase 1 (Preparation stage): Stage in which an additional        PUCCH saving cell is set.    -   3. Phase 2 (Execution stage): Stage in which type 2 handover is        executed and PCell is changed to a target serving cell. Here,        the serving cell is not PCell, but is a cell in which the PUCCH        is set.    -   4. Phase 3 (Completion stage): Stage in which the previous PCell        is released.

The type 2 handover includes a handover using a dual connectivity (DC)and RLC split bearer, a handover using DC and MAC split bearer, and aneCA-based handover. Hereinafter, an eCA-based handover procedure will bedescribed in detail.

FIGS. 4FA and 4FB are diagrams of a handover operation using eCA and aprotocol structure, according to an embodiment of the presentdisclosure.

Phase 0 corresponds to a stage in which the UE and a gNB are connectedto each other in an NR system to perform basic data transmissionreception (at 4 f-05). It is assumed that a source cell of the gNB iscomposed of one PCell and one SCell. In the above-described stage, thegNB configures an MCG bearer through which data is transmitted orreceived only with respect to the serving cell of the MeNB, and eachPDCP device is connected to one RLC device, and the MAC and RLC devicesare connected to each other using a logical channel (at 4 f-10). The UEsets the PDCP. RLC, and MAC in accordance with the bear setup with thegNB, and receives a control signal and data through the PCell (Cell1).Further, the UE transmits HARQ feedback, scheduling request, and CSI tothe PCell (Cell1) through the PUCCH, and performs datatransmission/reception through the SCell (Cell2). The SCell repeats anactive state and an inactive state in accordance with the indication ofthe eNB.

If it is determined that the gNB satisfies a specific condition and theeCA for the handover is required, the eCA is set in Phase 1 stage (at 4f-20). In the above-described stage, the gNB sets a PUCCH SCell group(target cell) composed of a PUCCH SCell (Cell3) and SCell (Cell4), anddetermines a handover to the corresponding target cell. Thereafter, thesource cell of the gNB performs eCA with the target cell includingadditional PUCCH serving cells Cell3 and SCell (Cell4) (at 4 f-25). Atthe above-described stage, the target PDCP setup and the RLC setup arenot performed, and in this case, the PDCP and RLC reconfigurationoperation is not necessary since handover operations are performed inthe same gNB. As the eCA is performed, the UE sets a new MAC in whichthe existing setup of the source cell is extended to include the targetcell with respect to the SRB and DRB (at 4 f-30). The MACreconfiguration may include HARQ setup, power headroom report (PHR)setup, primary time advance group (pTag), and second time advance group(sTag); this is because the eCA is used for the handover having nointerference, and thus S-MAC for dividedly transferring the DRBcorresponding to a specific EPC bearer ID is not reconfigured.

If the eNB receives an event corresponding to the handover from ameasurement report value of the UE, e.g., the signal strength from thetarget cell becomes better than the signal strength from the source cellover a threshold value, and in this case, Phase 2 is set to change theroles of the PCell (Cell1) and the PUCCH SCell (Cell3) each other (4f-35). In the above-described stage, the existing bearer setup is notchanged, but only the roles of the PCell and PUCCH SCell are changedwith each other. Due to this, MAC and RRC signaling reconfiguration isperformed (at 4 f-40). In the same manner as the eNB setup, the existingprotocol setup is maintained even in the UE, the roles of the PCell andPUCCH SCell are changed with each other, and the MAC is reconfigured (at4 f-45).

If the gNB receives an event related to the release of the eCA of thesource cell from a measurement report value of the UE, e.g., if thesignal strength from the source cell is reduced below the set thresholdvalue, Phase 3 is set to release the eCA (at 4 f-50). In this stage, thesource eNB transmits an SCell release request signal including an SCellindex for releasing the eCA connection to the UE, and performs MACreconfiguration related to the SCell to be released (at 4 f-55). The maxreconfiguration may include HARQ setup, PHR setup, pTag, and sTag. Inthe same manner, even the UE reconfigures the MAC, and performs datatransmission/reception in the newly set target cell (at 4 f-60).

FIGS. 4GA and 4GB are diagrams of a handover procedure using eCA,according to an embodiment of the present disclosure.

First, a stage (Phase 0) is assumed, in which a UE 4 g-01 receives (atstep 4 g-05) a downlink control signal and data and transmits (at step 4g-10) an uplink control signal and data in a state where the UE 4 g-01is connected to a source eNB 4 g-02 and a source cell 4 g-03. In thisstage, it is possible to receive the downlink control signal throughPCell included in the source eNB 4 g-02 and to transmit the controlsignal through the uplink, and in accordance with the indication of thesource eNB 4 g-02, the UE 4 g-01 performs an auxiliary datatransmission/reception through SCell.

The UE 4 g-01 measures neighboring cells periodically or in accordancewith the setup of the source eNB 4 g-02, and if a specific condition issatisfied, the UE 4 g-01 transfers a measurement value for notifying thecorresponding source cell 4 g-03 that eCA for a handover in the same eNB4 g-02 is necessary, and starts Phase 1 stage (at step 4 g-15). Themeasurement value measured by the UE 4 g-01 may include an event for acase where the signal strength from the source cell 4 g-03 becomeslowered and the signal strength from the target cell 4 g-04 becomesheightened, and the source cell 4 g-03 that has received this mayrecognize mobility of the UE 4 g-01, and may prepare the handover in thesame eNB 4 g-02. That is, the source cell prepares eCA-based type-2handover in the same eNB 4 g-02, and performs eCA setup so as to performthe handover to the target cell 4 g-04. If the source cell 4 g-03completes the eCA preparation stage, it transfers an rrcReconfigReqmessage to the UE 4 g-01 (at step 4 g-25). The message includes SCellsetup information of the target cell 4 g-04. That is, as the eCA isperformed, the UE 4 g-01 sets a new MAC in which the existing setup ofthe source cell 4 g-03 is extended to include the target cell 4 g-04with respect to the SRB and DRB. The MAC reconfiguration may includeHARQ setup, PHR setup, pTag, and sTag setup (at step 4 g-30).Thereafter, the UE 4 g-01 performs a random access procedure with thetarget cell 4 g-04 (at step 4 g-35), and performs uplink and downlinktransmission/reception with the source cell 4 g-03 and the target cell 4g-04 (at steps 4 g-40 to 4 g-55). Through the above-described Phase 1stage (at steps 4 g-15 to 4 g-55), the UE 4 g-01 is simultaneouslyconnected to the source cell 4 g-03 and the target cell 4 g-04 toperform data transmission/reception, and in this process, timeinterference does not occur.

After the Phase 1 stage, if the measurement value of the UE 4 g-01includes an event indicating the handover of the target cell 4 g-04 (atstep 4 g-60), the source cell 4 g-03 determines the handover to thetarget cell 4 g-04 (Phase 2 stage) (at step 4 g-65). The measurementvalue may include an event for a case where the signal strength from thesource cell 4 g-03 becomes lowered and the signal strength from thetarget cell 4 g-04 becomes heightened, and thus the events in an LTE fordetermining the handover may be reused, or a new event may be added. Ifthe source cell 4 g-03 receives the message, it does not change theexisting bearer setup, but changes the roles of PCell and PUCCH SCelleach other. Further, the source cell 4 g-03 transfers type-2 handovercommand to the UE 4 g-01 through an RRCConnectionReconfiguration (atstep 4 g-75). The RRC message implicitly or explicitly the setupindicating the change of the roles of PCell and PUCCH SCell each otherincluded in the source cell 4 g-03 and the target cell 4 g-04. The UE 4g-01 performs the type-2 handover to the PUCCH SCell of the target cell4 g-04 (at step 4 g-80), and transfers a type-2 handover complete RRCmessage to PCell of the source cell 4 g-03 and the PUCCH Cell of thetarget cell 4 g-04 (at step 4 g-80).

As the UE 4 g-01 performs the type-2 handover, it maintains the existingLayer 1 transmission/reception, and Layer 2 (MAC) cancels the existingset PHR, and controls the PH location of the PHR in accordance with thechange of PCell and SCell. Further, through the change to the PUCCHSCell, the existing PCell (Cell1) suspends the RAR reception in PCell(Cell) of the source cell 4 g-03, sets TAG to sTAG, and releases the setSPS. The PUCCH SCell (Cell3) of the target cell 4 g-04 starts the RARreception, sets TAG to pTAG, and monitors SPS cell-radio networktemporary identifier (C-RNTI). Further, it changes the bit location foractivation/deactivation of the MAC CE in accordance with the setSCellIndex. Further, Layer 3 controls the radio link monitoring (RLM)determining the RLF in accordance with the change of PCell and PUCCHSCell. That is, as the existing PCell (Cell1) is changed to the PUCCHSCell, it suspends the RLM operation and paging reception, and theexisting PUCCH SCell (Cell3) starts RLM and paging reception, and readsthe SFN to use the same as a reference. In the same manner, even thereport for the measurement value is controlled and reported inaccordance with the change of PCell and SCell, and ServCellIndex is alsocontrolled. For example, with respect to Cell1 (previous PCell), it ischanged to a specific value x at index 0, and with respect to Cell3(previous PUCCH SCell), it is changed to 0 at index y. The method forsetting the ServCellIndex of the previous PCell may be one of thefollowing methods.

-   -   Option 1: Type-2 handover command at step 4 g-70 or RRC        connection reconfiguration at step 4 g-25 explicitly transfers        SCellIndex.    -   Option 2: New PCell (Cell3) automatically allocates the used        SCellIndex.

Thereafter, the UE 4 g-01 maintains uplink and downlinktransmission/reception with the source CELL 4 g-03 and the target CELL 4g-04 (at steps 4 g-85 to 4 g-100). Through the above-described Phase 2stage (at steps 4 g-60 to 4 g-100), the UE 4 g-01 changes the roles ofPCell of the source cell 4 g-03 and PUCCH SCell of the target cell 4g-04 with each other, and is simultaneously connected to the two eNBs toperform data transmission/reception, and in this process, timeinterference does not occur.

After the Phase 2 stage, if the measurement value of the UE 4 g-01includes an event indicating the release of the source cell 4 g-03 (atstep 4 g-105), the target cell 4 g-04 determines the eCA release of thesource cell (Phase 3 stage) (at step 4 g-105). The measurement value maybe performed when the UE 4 g-01 determines that the signal strength fromthe source eNB 4 g-02 becomes lower than a specific threshold value andis not suitable to perform the communication. Events in an LTE for thismay be reused, or a new event may be added. The source eNB 4 g-02notifies the UE 4 g-01 of the release of SCell through the RRC message(at step 4 g-115). The SCell release as described above means eCArelease of Cell1 and Cell2. Thereafter, the UE 4 g-01 and the targetcell 4 g-04 maintains the uplink and downlink transmission/reception (atsteps 4 g-120 and 4 g-125).

FIG. 4H is a diagram of the terminal performing type-2 handoverprocedure using eCA, according to an embodiment of the presentdisclosure.

The UE performs uplink and downlink data transmission/reception (Phase0) with the source cell connected to the UE, and if the measurementvalue is changed due to the movement (at step 4 h-01 and 4 h-05), itreports the measurement value including the event kind to the sourcecell. The subsequent operation is determined in accordance with thecurrent state of the UE and the measurement value. A handover methodusing the eCA for the handover procedure in which time interferencebecomes 0 is proposed. If the measurement value corresponding to Phase 1occurs in a state where the UE operates in Phase 0, it transfers themeasurement value to the source cell (at step 4 h-10). Thereafter, ifthe source cell determines necessity of multi-connection and transferseCA setup information (at step 4 h-15), the UE receives this to performsetup for the eCA. The UE reconfigure the MAC in accordance with the setSCell-Config (SCellToAddMod) (at step 4 h-20). As the eCA setup isperformed, the UE sets a new MAC in which the existing setup of thesource cell is extended to include the target cell with respect to theSRB and DRB. The MAC reconfiguration may include HARQ setup, PHR setup,pTag, and sTag. Thereafter, the UE configures the eCA, and performuplink and downlink data transmission/reception through the PCell groupand the PUCCH SCell group (at step 4 h-25)

Through the above-described stage, the UE operates in Phase 1 state, andif an event indicating necessity of the handover to the target cell,that is, an event to perform Phase 2, occurs (at step 4 h-05), the UEreports the measurement value including the event kind to the eNB.Thereafter, the UE receives the RRC message indicating type-2 handoverfrom the eNB to the target cell (at step 4 h-30), and changes the rolesand setup of PCell and PUCCH SCell for the type-2 handover (at step 4h-35). As the eCA-based type 2 handover is performed, the UE maintainsthe existing Layer 1 transmission/reception, and Layer 2 (MAC) cancelsthe existing set PHR, and controls the PH location of the PHR inaccordance with the change of PCell and SCell. Further, through thechange to the PUCCH SCell, the existing PCell (Cell1) suspends the RARreception in PCell (Cell1) of the source cell, sets TAG to sTAG, andreleases the set SPS. The PUCCH SCell (Cell3) of the target cell startsthe RAR reception, sets TAG to pTAG, and monitors SPS C-RNTI. Further,it changes the bit location for activation/deactivation of the MAC CE inaccordance with the set SCellIndex. Further, Layer 3 controls the RMLdetermining the RLF in accordance with the change of PCell and PUCCHSCell. That is, as the existing PCell (Cell1) is changed to the PUCCHSCell, it suspends the RLM operation and paging reception, and theexisting PUCCH SCell (Cell3) starts RLM and paging reception, and readsthe SFN to use the same as a reference. In the same manner, even thereport for the measurement value is controlled and reported inaccordance with the change of PCell and SCell, and ServCellIndex is alsocontrolled. For example, in case of PCell of the existing source cell, xdesignated by SCellIndex is used, and in case of PUCCH SCell of theexisting target cell, the previous y index is not used, and the index isnot allocated. After the change of the roles of PCell and PUCCH SCell asdescribed above, the UE performs uplink and downlink datatransmission/reception through the eCA (at step 4 h-40).

Through the above-described stage, the UE operates in Phase 2 state, andif an event indicating necessity of the release of the source cell, thatis, an event to perform Phase 3, occurs (at step 4 h-05), the UE reportsthe measurement value including the event kind to the eNB (at step 4h-10). Thereafter, the UE receives the RRC message indicating the eCA ofthe source cell from the eNB (target cell) (at step 4 h-45), andreleases SCells (Cell1 and Cell2) related to the eCA of the existingPCell group (at step 4 h-50). In the stage, the UE reconfigures the MACaccording to the SCell release. Thereafter, the UE performs uplink anddownlink data transmission/reception through the target cell.

The UE may perform different operations in accordance with the cell towhich the UE itself belongs. In FIG. 4F, the eCA-based type-2 handoverprocedure composed of 4 Cells and the protocol structure have beendescribed. In Table 2 below, the operations of the UE before and afterit receives the type-2 handover command are summarized.

TABLE 2 Cell 1 Cell 3 Cell 2, 4 Before receiving type PCell PUCCH SCellSCell 2 HO command After receiving type PUCCH SCell PCell SCell 2 HOcommand Layer 1 (Cell group) UE continue the current UE continue thecurrent UE continue the operations on this cell; operations on thiscell; current operations on i.e. i.e. this cell; i.e. PUCCH/PUSCH txPUCCH/PUSCH tx PUSCH tx (if uplink is PDCCH/PDSCH rx PDCCH/PDSCH rxconfigured) PDCCH/PDSCH rx Layer 2 (MAC) Cancel triggered PHR Canceltriggered PHR Continue the current Change PH location in Change PHlocation in operations PHR PHR (Type 2 PH location (Type 2 PH locationand type 1 PH location) and type 1 PH location) stop RAR reception startRAR reception consider its TAG as consider its TAG as sTAG pTAG releaseSPS start to monitor SPS C- Update the mapping of RNTIActivation/Deactivation Update the mapping of MAC CE bit positionActivation/Deactivation (from no corresponding MAC CE bit position bitto b_x, x is (from b_y to no SCellIndex) corresponding bit) Layer 3(RRC) stop RLM start RLM Continue the current Evaluated as SCell forEvaluated as PCell for operations measurement measurement Stop pagingreception Start paging reception Update ServCellIndex read SFN and takeit for from 0 to x reference Update ServCellIndex from y to 0

UE behavior in each layer when type 2 HO command is received.

In the Layer 3 operation, the method for setting ServCellIndex of theprevious PCell may be one of the following methods.

-   -   Option 1: Type-2 handover command at step 4 g-70 or RRC        connection reconfiguration at step 4 g-25 explicitly transfers        SCellIndex.    -   Option 2: New PCell (Cell2) automatically allocates the used        SCellIndex.

The UE features can be summarized in comparison to type-1 handover. InTable 3 below, type-1 handover in the existing LTE and type-2 handoverusing eCA proposed in the present disclosure are summarized.

TABLE 3 Type 1 HO Type 2 HO Pre-step over the radio None PUCCH SCellgroup addition interface Post-step over the radio None PUCCH SCell grouprelease interface Triggering RRC message Type 1 HO command i.e. Type 2HO command i.e. rrcConnectionReconfigurationrrcConnectionReconfiguration with mobilityControlInfo (target withtype2HO indication cell id, target frequency, C-RNTI etc.) Cell id oftarget cell & in mobilityControlInfo in HO In SCell addition message inpre- ARFCN of target command message step frequency(rrcConnectionReconfiguration with mobilityControlInfo) L1 stop L1operation with source continue L1 operation with source start L1operation with target and target SCell Deactivate SCells except primaryDo not change SCell status except SCell (PSCell) PSCell Do not changePSCell status

A Type 1 HO and Type 2 HO.

FIG. 4I is a diagram of a terminal, according to an embodiment of thepresent disclosure.

Referring to FIG. 4I, the terminal includes an RF processor 4 i-10, abaseband processor 4 i-20, a storage unit 4 i-30, and a controller 4i-40.

The RF processor 4 i-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. That is, the RF processor 4 i-10 performs up-conversionof a baseband signal provided from the baseband processor 4 i-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 4 i-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, and an ADC. Although only one antenna is illustratedin FIG. 4 i , the terminal may be provided with a plurality of antennas.The RF processor 4 i-10 may include a plurality of RF chains. The RFprocessor 4 i-10 may perform beamforming, and for the beamforming, theRF processor 4 i-10 may adjust phases and sizes of signals transmittedor received through the plurality of antennas or antenna elements. TheRF processor may perform MIMO, and may receive several layers duringperforming of a MIMO operation.

The baseband processor 4 i-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the system. During data transmission, the baseband processor 4 i-20generates complex symbols by encoding and modulating a transmitted bitstring. During data reception, the baseband processor 4 i-20 restores areceived bit string by demodulating and decoding the baseband signalprovided from the RF processor 4 i-10. When following an OFDM method,during data transmission, the baseband processor 4 i-20 generatescomplex symbols by encoding and modulating a transmitted bit string,performs mapping of the complex symbols on subcarriers, and thenconfigures OFDM symbols through the IFFT operation and CP insertion.During data reception, the baseband processor 4 i-20 divides thebaseband signal provided from the RF processor 4 i-10 in the unit ofOFDM symbols, restores the signals mapped on the subcarriers through theFFT operation, and then restores the received bit string throughdemodulation and decoding.

The baseband processor 4 i-20 and the RF processor 4 i-10 may be calleda transmitter, a receiver, a transceiver, or a communication unit. Inorder to support different radio connection technologies, at least oneof the baseband processor 4 i-20 and the RF processor 4 i-10 may includea plurality of communication modules. In order to process signals ofdifferent frequency bands, at least one of the baseband processor 4 i-20and the RF processor 4 i-10 may include different communication modules.The different radio connection technologies may include a radio LAN(e.g., IEEE 802.11) and a cellular network (e.g., LTE). Further, thedifferent frequency bands may include SHF (e.g., 2.5 GHz or 5 GHz) bandand millimeter wave (mmWave) (e.g., 60 GHz) band.

The storage unit 4 i-30 stores a basic program for an operation of theterminal, application programs, and data of setup information. Inparticular, the storage unit 4 i-30 may store therein informationrelated to a second access node performing wireless communication usinga second radio connection technology. The storage unit 4 i-30 providesstored data in accordance with a request from the controller 4 i-40.

The controller 4 i-40 controls the terminal. The controller 4 i-40transmits and receives signals through the baseband processor 4 i-20 andthe RF processor 4 i-10. The controller 4 i-40 records or reads data inor from the storage unit 4 i-30. For this, the controller 4 i-40 mayinclude at least one processor, and may include a communicationprocessor for communication and an AP for controlling an upper layer,such as an application program.

FIG. 4J is a diagram of a base station in a wireless communicationsystem, according to an embodiment of the present disclosure.

The base station includes an RF processor 4 j-10, a baseband processor 4j-20, a backhaul communication unit (communication unit) 4 j-30, astorage unit 4 j-40, and a controller 4 j-50.

The RF processor 4 j-10 performs transmitting and receiving a signalthrough a radio channel, such as signal band conversion andamplification. That is, the RF processor 4 j-10 performs up-conversionof a baseband signal provided from the baseband processor 4 j-20 into anRF-band signal to transmit the converted signal to an antenna, andperforms down-conversion of the RF-band signal received through theantenna into a baseband signal. The RF processor 4 j-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a DAC, and an ADC. Although only one antenna is illustratedin the drawing, the first connection node may be provided with aplurality of antennas. The RF processor 4 j-10 may include a pluralityof RF chains. The RF processor 4 j-10 may perform beamforming, and forthe beamforming, the RF processor 4 j-10 may adjust phases and sizes ofsignals transmitted or received through the plurality of antennas orantenna elements. Further, the RF processor may perform down MIMOoperation through transmission of one or more layers.

The baseband processor 4 j-20 performs conversion between a basebandsignal and a bit string in accordance with the physical layer standardof the first radio connection technology. During data transmission, thebaseband processor 4 j-20 generates complex symbols by encoding andmodulating a transmitted bit string. During data reception, the basebandprocessor 4 j-20 restores a received bit string by demodulating anddecoding the baseband signal provided from the RF processor 4 j-10. Whenfollowing an OFDM method, during data transmission, the basebandprocessor 4 j-20 generates complex symbols by encoding and modulating atransmitted bit string, performs mapping of the complex symbols onsubcarriers, and then configures OFDM symbols through the IFFT operationand CP insertion. During data reception, the baseband processor 4 j-20divides the baseband signal provided from the RF processor 4 j-10 in theunit of OFDM symbols, restores the signals mapped on the subcarriersthrough the FFT operation, and then restores the received bit stringthrough demodulation and decoding. The baseband processor 4 j-20 and theRF processor 4 j-10 may be called a transmitter, a receiver, atransceiver, or a wireless communication unit.

The communication unit 4 j-30 provides an interface for performingcommunication with other nodes in the network. That is, thecommunication unit 4 j-30 converts a bit string transmitted from themain eNB to another node, for example, an auxiliary eNB or a corenetwork into a physical signal, and converts the physical signalreceived from the other node into the bit string.

The storage unit 4 j-40 stores t a basic program for an operation of themain base station, application programs, and data of setup information.In particular, the storage unit 4 j-40 may store information on a bearerallocated to the connected terminal and the measurement result reportedfrom the connected terminal. The storage unit 4 j-40 may storeinformation that becomes a basis of determination whether to provide orsuspend a multi-connection to the terminal. Further, the storage unit 4j-40 provides stored data in accordance with a request from thecontroller 4 j-50.

The controller 4 j-50 controls the main base station. The controller 4j-50 transmits and receives signals through the baseband processor 4j-20 and the RF processor 4 j-10 or through the backhaul communicationunit 4 j-30. The controller 4 j-50 records or reads data in or from thestorage unit 4 j-40. For this, the controller 4 j-50 may include atleast one processor.

While the present disclosure has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the scope of the present disclosure. Therefore,the scope of the present disclosure should not be defined as beinglimited to the embodiments, but should be defined by the appended claimsand equivalents thereof.

What is claimed is:
 1. A method performed by a terminal in a wirelesscommunication system, the method comprising: receiving a first radioresource control (RRC) connection release message for transitioning intoan RRC inactive state, the first RRC connection release messageincluding a resume identity and a next hop chaining count; in case thatuplink data occurs in the RRC inactive state, transmitting, to a basestation, a random access preamble; receiving, from the base station, arandom access response including timing alignment information and anuplink grant; transmitting, to the base station, a single medium accesscontrol (MAC) protocol data unit (PDU) including the uplink data and anRRC connection resume request message, the RRC connection resume requestmessage including the resume identity; and receiving, from the basestation, a second RRC connection release message as a response to theRRC connection resume request message, wherein the random accesspreamble is selected from a preamble group for transmitting the uplinkdata associated with a data radio bearer (DRB).
 2. The method of claim1, wherein a threshold for the uplink data is obtained based on systeminformation, and wherein the random access preamble associated with theuplink data is transmitted in case that a size of the uplink data isless than or equal to the threshold.
 3. The method of claim 1, whereinthe uplink data associated with the DRB is multiplexed with the RRCconnection resume request message associated with a signaling radiobearer (SRB) in the single MAC PDU.
 4. The method of claim 1, wherein akey is derived based on the next hop chaining count included in thefirst RRC connection release message, and wherein the uplink data isciphered based on the key.
 5. The method of claim 1, wherein the RRCconnection resume request message includes a short messageauthentication code-integrity (MAC-I), and wherein the uplink data istransmitted to the base station with no transition to an RRC connectedstate from the RRC inactive state.
 6. A method performed by a basestation in a wireless communication system, the method comprising:receiving, from a terminal, a random access preamble associated withuplink data for the terminal, the terminal being in a radio resourcecontrol (RRC) inactive state based on a first RRC connection releasemessage including a resume identity and a next hop chaining count;transmitting, to the terminal, a random access response including timingalignment information and an uplink grant; receiving, from the terminal,a single medium access control (MAC) protocol data unit (PDU) includingthe uplink data and an RRC connection resume request message, the RRCconnection resume request message including the resume identity; andtransmitting, to the terminal, a second RRC connection release messageas a response to the RRC connection resume request message, wherein therandom access preamble is selected from a preamble group fortransmitting the uplink data associated with a data radio bearer (DRB).7. The method of claim 6, wherein a threshold for the uplink data isobtained based on system information, and wherein the random accesspreamble associated with the uplink data is transmitted in case that asize of the uplink data is less than or equal to the threshold.
 8. Themethod of claim 6, wherein the uplink data associated with the DRB ismultiplexed with the RRC connection resume request message associatedwith a signaling radio bearer (SRB) in the single MAC PDU.
 9. The methodof claim 6, wherein a key is derived based on the next hop chainingcount included in the first RRC connection release message, and whereinthe uplink data is ciphered based on the key.
 10. The method of claim 6,wherein the RRC connection resume request message includes short messageauthentication code-integrity (MAC-I), and wherein the uplink data istransmitted to the base station with no transition to an RRC connectedstate from the RRC inactive state.
 11. A terminal in a wirelesscommunication system, the terminal comprising: a transceiver; and acontroller configured to: receive, via the transceiver, a first radioresource control (RRC) connection release message for transitioning intoan RRC inactive state, the first RRC connection release messageincluding a resume identity and a next hop chaining count, in case thatuplink data occurs in the RRC inactive state, transmit, to a basestation via the transceiver, a random access preamble, receive, from thebase station via the transceiver, a random access response includingtiming alignment information and an uplink grant, transmit, to the basestation via the transceiver, a single medium access control (MAC)protocol data unit (PDU) including the uplink data and an RRC connectionresume request message, the RRC connection resume request messageincluding the resume identity, and receive, from the base station viathe transceiver, a second RRC connection release message as a responseto the RRC connection resume request message, wherein the random accesspreamble is selected from a preamble group for transmitting the uplinkdata associated with a data radio bearer (DRB).
 12. The terminal ofclaim 11, wherein a threshold for the uplink data is obtained based onsystem information, and wherein the random access preamble associatedwith the uplink data is transmitted in case that a size of the uplinkdata is less than or equal to the threshold.
 13. The terminal of claim11, wherein the uplink data associated with the DRB is multiplexed withthe RRC connection resume request message associated with a signalingradio bearer (SRB) in the single MAC PDU.
 14. The terminal of claim 11,wherein a key is derived based on the next hop chaining count includedin the first RRC connection release message, and wherein the uplink datais ciphered based on the key.
 15. The terminal of claim 11, wherein theRRC connection resume request message includes a short messageauthentication code-integrity (MAC-I), and wherein the uplink data istransmitted to the base station with no transition to an RRC connectedstate from the RRC inactive state.
 16. A base station in a wirelesscommunication system, the base station comprising: a transceiver; and acontroller configured to: receive, from a terminal via the transceiver,a random access preamble associated with uplink data for the terminal,the terminal being in a radio resource control (RRC) inactive statebased on a first RRC connection release message including a resumeidentity and a next hop chaining count, transmit, to the terminal viathe transceiver, a random access response including timing alignmentinformation and an uplink grant, receive, from the terminal via thetransceiver, a single medium access control (MAC) protocol data unit(PDU) including the uplink data and an RRC connection resume requestmessage, the RRC connection resume request message including the resumeidentity, and transmit, to the terminal via the transceiver, a secondRRC connection release message as a response to the RRC connectionresume request message, wherein the random access preamble is selectedfrom a preamble group for transmitting the uplink data associated with adata radio bearer (DRB).
 17. The base station of claim 16, wherein athreshold for the uplink data is obtained based on system information,and wherein the random access preamble associated with the uplink datais transmitted in case that a size of the uplink data is less than orequal to the threshold.
 18. The base station of claim 16, wherein theuplink data associated with the DRB is multiplexed with the RRCconnection resume request message associated with a signaling radiobearer (SRB) in the single MAC PDU.
 19. The base station of claim 16,wherein a key is derived based on the next hop chaining count includedin the first RRC connection release message, and wherein the uplink datais ciphered based on the key.
 20. The base station of claim 16, whereinthe RRC connection resume request message includes short messageauthentication code-integrity (MAC-I), and wherein the uplink data istransmitted to the base station with no transition to an RRC connectedstate from the RRC inactive state.